See, I told you the right one would come along.
If you haven’t gotten the hitch and brakes yet, try a trailer dealer who specializes in trailer maintenance rather than sales. You will need this person/firm for yearly maintenance anyway. You should also be able to find someone whose primary business is hitches. In a pinch, U-Haul will be able to do it. Just check the plug on the trailer so you can tell them the kind of adaptor.