Ostrich (Burgers and steaks) are getting more common certainly, had it a fair bit over the years and it's quite nice. I've had Bison and Buffalo burgers which I didn't find much difference in, I would say both are nicer than beef but it could also just be down to the cooking.
I know of an online store that sells the more exotic meats but it's fairly expensive unless you buy in reasonable quantity, which I can't afford right now. Quite a selection:
Alpaca, Bison, Buffalo, Camel, Crocodile, Elk, Goat, Horse, Iberico Pork, Kangaroo, Llama, Mouflon, Ostrich, Python, Reindeer, Veal, Springbok, Wagyu, Wild Boar, Zebra.
Crocodile and Kangaroo are the two that I've most often been on the lookout for in shops.