There was one near co-op city, but it closed a few years ago.

There are also several specialty book stores, e.g. the NY Botanical Garden has a really good one, there is a Jewish bookstore in Riverdale, etc.

Because The Bronx was largely designed for residential housing, it's very easy to just hop on the subway or in a car and get to a bookstore in a few minutes. It's actually much easier to get from The Bronx into Manhattan or into Westchester, Fairfield County, New Jersey, etc. than it is to get to other parts of The Bronx. So other than that some people seem to be morally offended by the fact that there isn't a general purpose bookstore in the borough, there isn't really any especially good reason to have one.