How many panda bears live in the U S?

Neither of the panda species are native to the US.

And particularly the Giant Panda is difficult to get to breed in captivity.

All Giant Pandas outside China are on loan from China, and AFAIK none have bred outside China.

The Red AKA Lesser Panda is less fickle, and there may well be a few of those that have bred in US parks and zoos.