I have a large oval one but I haven't seen any for sale in a long time. They're very pretty.
Best bet would be to email around a bit - Rick at Art Cut Gems is an opal specialist but I don't know if that is just the usual types or the more obscure ones as well.
They have tons, I just did not have the time to go past page 15. The best one they once had I, obviously, missed and now regret it. But if you go through all 41 page, you may find what you like.