First, I'd suggest going to Seahorse Source's Group on Facebook and then click on the "FILES" link. There is help there you can access to try to be successful at raising fry. It's not easy and it can be labour intensive, but until you succeed you don't have to worry about where to sell any.
Selling livestock on Facebook though is a NO-NO and Facebook shuts down any site that allows a post about seahorses for sale.
I don't know what the forum policy is here but I do know that many fry end up being sold to LFS's but the value offered is usually quite low.