ya I see them all the time in random LFS's around Pittsburgh....I thought it was illegal to sell ALL natives in PA, regardless of classification as game or rough...I must be wrong on channels though because I've seen them in multiple locations.You can find them at most Ma & Pa LFSs but if you want a different selection of sizes, morphs, etc your best bet is contact your local state fish hatchery. Channel catfish are practically considered "gamefish" in many states and thus are bred prolifically by many states. If you are in PA, I know for a fact you can find them at hatcheries
For people in SE, SC, NE, and NC PA : http://kurtzlivebaitvending.com/
P.S. I contacted 4 hatcheries in PA to see if they'd sell me a couple different species, no dice. They were very quick to shut me down on purchasing natives.