It's easy to do on your own. Classic buffalo sauce is just Frank's Red Hot and butter. Dip the parts of your rotisserie bird as you remove them for the best texture.
I have seen premade buffalo roast chicken at the deli plenty of times. But that's more uniform for slicing onto sandwiches, not the same as rotisserie meat.
Franks is a classic but anyone I know makes better buffalo sauce using Crystal hot sauce and butter. It's a bit less acidic. That deli counter buffalo roast chicken is weirdly good also.