I did a google check and came up empty. Guess you'll have to grow your own.

Here is a link to a group that's doing research on the Soldier Fly. They don't say anything about selling them but they might be able to give you some information.

Here is a link that might be useful: Bio-Conversion of Putrescent Wastes

how many do you want?

How many you got?

I'd say about a quart would be good.

Since it is the season for these creatures to be prolific, why not do a "build it and they will come"? I know if I were to put a lot of OM in a bin environment and let it be for a short time, I find them in mass. Wa La!

Are they fairly common in the Southeastern U.S.?

Common and in mass here in Raleigh, NC, especially this time of year. If you have warm temps, lots of OM, you too will have BSF's in no time.

I ran into several wriggling masses of them in my compost pile today. Despite it being pretty hot in there, they were chomping on the food waste. (Had a bit too much for the worms at once)

Yeah, I have a compost tumbler, and my neighbor filled it up with grass clippings the other day. Needless to say, it was a little overwhelmed with all that fresh green OM, so I just wet it down and left it. Have been adding extra kitchen scraps..after worms have had theirs...and I had hundreds of the little soldier fly larva in there within just a couple days. I live in Charlotte NC, so I guess they are pretty comfortable in the southeast.