Daphnia (in several species) are so much easier to raise as live foods, gammarous (also in several species) aren't really worth the bother.

Fishing bait dealers will sometimes carry a large gammarous species for bait. Somebody way up north must have dedicated a big old pond or old swimming pool out in the woods to their culture. Those gammarous - also called scuds - probably could take a guppy two out of three.

Smaller scuds (not the missiles) will also live beneath a u.g. filter plate (at least one without bleach), work through the gravel, and provide tank residents with a surprise snack.