Here’s a list of a WordPress theme shops ordered by Alexa rank.
I was surprised to find a few near the top I haven’t heard of before. A few near the bottom are defunct or no longer maintained.
WordPress Theme Shops
136 theme companies as of July 17, 2013.
If you see one I’ve missed, drop it in the comments.
That list is nearly a year old. To quote Neil DeGrasse Tyson on Cosmos, that’s barely a second on the online cosmic calendar.