Well, any relative of the goldfish in America is invasive. Unless you're in an area that is highly ecologically disturbed and the native species populations damaged, you shouldn't see many goldfish or carp swimming around (there are plenty of places where you do, but garters evolved without them there). I would say that trout and trout relatives are probably most common in rivers in my area, and in slower-moving water crappie and bluegill are very common. I believe those are all thiaminase-free species?
Most species that are fish specialists in the wild can still be taught to eat pinkies in captivity though, like ribbon snakes.

Thiaminase poisoning is typically a long-term process (though I imagine some snakes may be more sensitive than others). If the snake were eating a balanced diet and not JUST one species of thiaminase-containing fish, I would imagine it could get well into its reproductive years before noticing any effects, maybe even live a natural lifespan and die of predation or disease. Of course, in the wild this would probably happen in the first five years or so, which is pretty short compared to a captive garter. That being the reason keepers can be so paranoid about the thiaminase issue, since we want them to live as long as possible