"Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same." - President Ronald Reagan
You can get them mail order, but I don't think they live this far north. They are a tropical fly and I don't think they can overwinter where it freezes.
Once it warms up, or if you have a heated greenhouse, you can keep them.
In general the warmer and wetter your climate, the more likely it is that you already have black soldier flies in your area. Colder and drier climates represent the least likely places to find BSF and they are the most challenging places to establish a colony. This is also true of elevations over 5000 feet (1500m). The native range of BSF is the southeastern U.S. but over time they have been transported around the world. BSF are most commonly found in the USDA plant hardiness zones 7 – 10.
"Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same." - President Ronald Reagan
"Modern agriculture specializes in the use of land for the conversion of petroleum to food.
Sustainable agriculture is something your great grandchildren will be able to do regardless of the inputs. Time tests all methods." Keith Mikkelson