I've been past deer farms in Scotland, and bought venison from Sainsbury's, so it's not THAT unusual and exciting.
(I'm sure I've seen rabbit in the freezer section, too.) I think the "not quite so PC"-ness of a lot of exotic meat is why most major chains stopped selling kangaroo and ostrich and what-have you. I did see crocodile on sale in a restauruant I visited recently, though - I think it was Old Orleans? A chain one, anyway.
Sadly, a lot of exotic animals like crocodiles are only tolerated in some countries if they can be useful - a case of "if we can't use it, it's not worth the risk of letting it stay in the area". And it's better to farm them and preserve the species than to simply hunt them and drive them to extinction, I suppose. The idea of eating a guinea-pig is a bit surreal, since a friend of mine just got one, and I can imagine her wanting to eat it, now. :P
I'd dispute that it's much harder to get all your protein from vegetable sources - it's easy to be LAZY and not eat enough VARIED vegetables, (only soy is a complete source of all eight essential amino acids) but so long as you're careful and eat a variety of beans, nuts, seeds, cereals and leafy vegetables you can get all eight essential amino acids from a purely plant-based diet. Generally, combine a legume with a nut or a seed and you get all eight. It's just iron and vitamin B12 that are harder to come by - animal-based iron is in the form of "heme" and can be absorbed, plant-based iron is not (I think it's bound up in chlorophyll, or something?) and can not be absorbed. And of course, plants don't contain cholesterol (although a lot DO contain high levels of fat - like parsnips, apparently. *blech*)
Quorn IS fairly grim, though; unless you disguise the taste with tomato or herbs or something. I vaguely remember having a Quorn burger - minced cardboard shaped into a circle, it seemed like.