I like my Marcos Heguy from Danny's Tack in Tully, NY. I went with the full suede and it's actually my boss's favorite, too.
The Tackeria sells a wide range of saddles, including used. With their reputation they don't sell anything junky. I would have confidence ordering used from them.
Texas Polo sells a wide variety of new, but I don't know about used.
There are several on ebay
My boss buys from different outlets because he then donates to colleges and clubs for students. The only ones we've been disappointed in were from India. We've ordered online from Argentina (I say we because he tells me to find and order them) and have been very happy.
The only thing to watch for when buying from South America is to verify that the saddle has billets and not only the rings for latigos. My Marcos Heguy has both.
Good luck and have fun!