Googled for Amiga hardware devs, found 5, but it said 0/5 were available for petitioning.
The ACA's can be bought online and cost 75 pound notes more than what you are prepared to see fly from your wallet. They have more advantages and are at least fully supported by the manufacturer.
A good way to test the market for a need you see is to talk to established hw devs on forums and together with them start a poll with binding pre-payments for a sum they could make a batch for. Problem is all but one are not full-time hw devs and have to do this as their work and family allows. And the one, Individual Computers, makes small batches of one expansion type at a time that have good chances of selling out.