I hope we can help, but we may need a bit more information from you.
Perhaps you have posted it before, but each board is separate.

1. What is the step-brother's given name? There are several ways of searching, but a name really helps. If you cannot give the name, do you have an approximate date of birth?

2. Do you know to which Virginia city/county Virgil moved? This will be the target research area AFTER 1930.

3. Can you find the year (at least) of Virgil's death, assuming he is deceased?
Depending on the year and area, an Obituary MAY list living relatives.
With the year, a Social Security Death Index search will be easier. With the month, you can order a death certificate in most states (for your Mom).
This will also give you a MONTH window to have a researcher (or volunteer) search for an obituary.

4. Do you know the name of this step-brother's mother? Her obituary may also list living relatives, including her son.

5. Siblings may also have been close enough to warrent mention of their brother / step-brother in their obituary.

So, you need to follow the FAMILY, not just one person. Fortunately, no matter how much we try, we are NOT islands. Most of us really do live in a community of relatives and friends.
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"Looking for information on ... James Virgil Gardner
a) born in 1899 in Sixpound-Warren County North Carolina.
b) moved to Virginia AFTER 1930. "

Did you locate him in the 1930 census?
Could he have been 'on the way to Virginia' ?

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1930 Census (River, Warren, NC)
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Someone named VIRGIE Gardner is living with wife Willie? Gardner. They have been married for 8-9 years and have three children: James, Mary, Carie and Birtha (sic).

Is this your Virgil?

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1920 Census (Little River, Warren, NC)
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Virgil Gardner - River, Warren, North Carolina, born about 1895. It MAY be the right one, since he is listed as born in NC. He is a boarder and working in the saw mills.

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Death Record
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*A Richard Gardner died in 1921 in Sixpound, NC.
Spouse was Lucy Gardner; Mother was Caroline.
Informant was William Gardner of Norfolk, VA. The Undertaker was William H. Gardner of Norfolk (son?? / grand-son?)
*Note NORFOLK!
If this IS the son, would he not know his mother's maiden name and put it on the death record (in his professional capacity)?

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WWI Draft Registration
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"Vergin" Gardner registered in Duplin county NC. His nearest relative was Lucy Gardner of Warren, NC.

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1910 Census (Sixpound, Warren, NC)
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James V. Gardner is 11 years old and living with Richard and Lucy, who are 'mis'(?) named as grandparents.
Carrie is the only other child (daughter) in the household. Lucy was married twice and had 5 living children of 10 born.

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1900 Census (Sixpound, Warren, NC)
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Virgil is the 2 year old son of Richard and Lucy Gardner. Other siblings in the household are William, Hattie, Carrie, and John. Lucy had 8 living children (of 10 born).
Four children are out of the 1900 household.

One additional child was Anna (Gardner) Turner, who died in Warren NC. She was born about 1887. Her parents were Richard Gardner and Lucy Robertson.

She is not recognized by that name in the family's 1900 census entry.

[This led to a search down this line.]

Annie G. Turner was the wife of Richard Turner. They lived in Sixpound, Warren in 1930 with 7 children.

In 1920, they are in River, Warren, NC with 6 children.

In 1910, they are in Sixpound, living with Thomas Gardner (57), and his wife, Mollie.
Annie G. Turner (22) is listed as his COUSIN, as are her first two children.

In 1900, 12 year old Annie Gardner is living with Cousin Thomas W. Gardner and his wife, Mary.

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1880 Census (Six Pound, Warren, NC)
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Richard Gardner and Lucy are found with two children, baby Bessie, and Eddie "Majho", her child from a previous marriage.

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1870 Census (Littleton, Warren, NC)
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As you know, Richard and his family are listed with Thomas, including his mother Caroline and at least two of his (probable) siblings, Priscilla and Minerva.

This summary is important to give others enough information to help in your search (excluding 1870).
Who were the people in Virgil's life?

Which relatives may have living descendants that would be easier to follow?

Finally, which relatives were a part of his CORE family group until he moved away.

Did he move to Virginia because a related was already there?

If so, then we know from the records that 'A' William was in Norfolk in 1921 - and MAY have worked in the funeral business. How may other relatives were in the area by 1930?

A 'cousin', Nettie Boyd, is listed in the Social Security death index for Richmond, Virginia.

Her sister, Martha Turner Palmer, has a North Carolina death record. Her parents were Richard and Annie Gardner Turner.

There are two other siblings that MAY be still living, or have living relatives (still) in Warren.

I guess the main point is to EXPAND your search. Although you may NOT find your grand-father DIRECTLY, you can find out ABOUT him. This will lead you to relatives you never knew you had - AND ONE of them may know where you can find your uncle or one of his family members.

Sometimes in genealogy, answers come when you are looking elsewhere.