Those folks you asked about bellies weren't butchers. If they don't know where bacon comes from, they need to get a new job. Most grocery stores don't employ real meat cutters these days, which is a shame. Everything is cut up at the packing plant and the grocers are just dressing it up and stamping their brand on it.
The butcher is the bbq'er's best friend. If you find a good one, make friends with him and he will always take care of you. If you don't have a legit grocery store (usually local owned) who actually cut their own meat, search your area for a meat-locker. Those guys will point you in the right direction. And as always, hit up the local farmers for the freshest and the best. You'll get a good deal most of the time if you are buying a whole animal. Go in with a bbq buddy and whole hog it.