I had the same issue with finding a good supply of earthworms.
Then I found Bunnings, $27.00 garden worm booster box 500 worms and an $8 worm farm container. Viola grow your own food, feed the worms some of your kitchen scraps and you also get an organic liquid fertilizer in the bottom of the container which can be used on your garden and indoor plants.
My fat little axies love there worms.
You could also try you local pet store they sometimes have small containers with the crickets for around $6 but very small worms and very few.
Good luck
Nat