I have had great luck at the Shoprite in Monticello NY for steamers. They have been superb for the last two weeks. I don't know about other Shoprite fish departments. BTW this same store has the best large lobsters and run sales at $6.99/lb at times.
NW has frozen bellies in the display case. Since they sell whole bellies on the take-out menu they must have them. Jfood would imagine if you asked they would have them on the wholesale side but you may be required to purchase more than even a real CH could eat in a sitting.