Set up a 10 or 15 gallon tank, some java moss and a sponge filter.
They plonk a few guppies in there and let them breed. Of course feed generously with only the best food. And hey-presto, you have your own free yet safe source of small feeders.
However you want to slowly introduce them to krill and such foods over time.
And your eventual goal should be to get them on manufactured foods.
But for the time being, all you want them to do it actually eat!