If a
local pet shop is selling them, and your climate is amenable, you're all set. Just set up your bin and drop them in. Be sure that you let some of the "crawl off" of mature grubs sit undisturbed in the soil or mulch....somewhere out of the reach of birds, so that they will hatch into adult flies and repeat the cycle. It took me a couple of years and a couple of introductions from outside to get them started here, but I am in a dry climate with only a few niches damp
enough for them. They need some moisture and access to
water as adults. There are also plans available for breeding them the complete cycle in an enclosure, such as a screenhouse or
greenhouse. The space needs to be big enough and bright enough for the adults to fly around and mate.