The Republican Party is trying to increase its share of the black vote, but most black voters seem unwilling to vote for a conservative black person. The black Republicans with the highest name recognition are Colin Powell, Condi Rice, and Clarence Thomas, none of whom have ever won an election. We wouldn't want Thomas to leave the Court, I doubt Condi would help the ticket win, and Powell was disloyal to Bush (keeping quiet when the Valerie Plame business was damaging Bush, when Powell knew who really leaked her name).
J. C. Watts might help in Oklahoma, but if the Republicans have to worry about Oklahoma, the situation is hopeless...it would be like naming Romney as VP candidate to be sure of carrying Utah.