I haven't found a supplier either. Which is odd because I think they are a fairly common fish in the aquaculture world.
The HBC are raised by the tens of millions in the south....for food fish growers. They sell them at 8" and they weigh about what a 4" fish would. Food growers want numbers, so fingerling producers starve the fish before selling them.
Since I used catfish growers to raise my Tilapia, I could get Hybrid Blue/Channel Catfish at about any size.