You can get it in Health Food Stores (maybe some larger grocery stores?) in the refrigerated section, "White Wave" is the only brand I know there. It will need seasoning or cooking in a sauce or breading and frying or adding to stir fry to make it very tasty. It's very bland and a bit rubbery, but versatile.
Also in Asian markets, you can get canned items, these are a much different texture and sometimes very flavorful, you just have to get past the whole "canned" idea. A good brand is "Companion" with a smallish can with a Blue, gold and red label. The "mock duck" and "mock abalone" are good and just little brown chunks in a gravy/broth.
The companies "Loma Linda" and "Worthington" also make some canned seitan/gluten products available in health food stores, and many regular grocery stores, and while they take MUCH more "getting used to" (they look VERY strange) some of the products are actually (surprisingly!!) VERY tasty and worth trying.