Any of the big names work. In some states there is sales tax but I found buying from golden state mint avoids that (cheapest option is to mail them a check rather than pay with card).

There may be some other sited that avoid tax, but if your state doesn't charge tax, apex, jmbullion, and any other big name bullion dealer is fine.

I bought all my gold from a reddit community (LOTS of jewlery at a bit above melt value, a few coins, etc)

My local coin shop