You can try collecting wild ones and see how they do in your vermicomposting setup. Don't get the big night crawlers, they need it too cool but the small/medium sized ones that come up when it rains might do the trick for you. Look on pavement after it rains or put down some damp
hay and collect under it a few times. You can even buy some at the fish bait places, they were grown in someone else's vermicomposting, after all! I think "trout worms" are the same thing as red wigglers usually.