Found this wonderful information at NARA:
Registro Central de Esclavos (Central Slave Registrar) and the 1872 Slave Census
Slavery was a fact of life in Puerto Rico until the passing of Moret Law in 1870. This edict granted freedom to slaves over 60, those belonging to the state, and children born to slaves after 9/17/1868. Most importantly for genealogy purposes, the Moret Law established the Central Slave Registrar which in 1872 began gathering the following data on the island's slave population: name, country of origin, present residence, names of parents, sex, marital status, trade, age, physical description, and master's name. There are eight microfilm rolls available, organized by the geographical districts, then by city. There is no information for District 3.
District 1 - Dorado, Naranjito, Trujillo Alto, Trujillo Bajo, San Juan
District 2 - Arecibo, Camuy, Ciales, Hatillo, Manati, Morovis, Quebradillas, Utuado
District 4 - Anasco, Cabo Rojo, Mayaguez
District 4 - Mayaguez (cont.), Sabana Grande, San German
District 5 - Adjuntas, Barros, Coamo, Guayanilla, Penuelas, Yauco, Juana Diaz
District 5 - Barranquitas, Ponce
District 6 - Arroyo, Guayama, Cidra
District 6 - Cidra (cont.), Aguas Buenas, Caguas, Cayey, Gurabo, Hato Grande (San Lorenzo), Salinas, Sabana del Palmar (Comerio)
Will be combing these records soon.