Try the wholesalers. They do supply private people, or small businesses, like a law firm. Maybe consolidate an order between a few of you.

Places like US Foods and Sysko Foods. They have amazing fresh fish and if you buy 2 or three kilos, you can ask them to "fillet and send all", which means they fillet it for you, and send you the bones etc. You can freeze it because you got it fresh, and it should be less expensive than retail.

Good luck