I will respond to the last part of your question first:

>Who would I need to test to find my paternal paternal great
>grandmother if my grandfather is deceased along with his siblings from
>his mother.I have yet to any find her ,Clara Harris on any censuses.I
>have checked for her on both the 1880,1900 Arkansas county,Arkansas
>censuses to no avail.

If your grandfather had a sister who had children, any of her children could be tested. If none of her children are living, but she had a daughter who had children, those grandchildren could be tested.

Here is a partial answer to your other question:
>Does any of the DNA testing companies have any data that can
>determine Mexican or Spanish heritage mixed with ones African
>heritage like from states of Georgia,Florida,Louisiana and Texas?

"Mexican" could be a mix of Native American, European, and African of varying percentages. Spanish would be the European component generally for the earlier time periods.

toot