https://www.triopsking.de/ is slow to the states, but lots of species and great prices.
Get a super tiny tank (~1 gallon), a water heater, SPRING water (not distilled they need minerals to healthily molt), and some SPRINULA (https://www.amazon.com/gp/product/B00WAPA2NS/ cheapest)
Eggs in. A TINY TINY TINY TINY amount of Spirulina per day or two, as they get bigger more, then you can switch in a few weeks to pellets, and move them into a bigger tank with a sponge filter if you want. Spring water only, though! I've found sudden transitions to different water can kill them, so make sure it's just spring.