One actually, they can reproduce without company. I started out with 10 - 15. Purposely overfed to have them multiply so I could put them in all of my tanks. I now control the population by not overfeeding. There is still enough in the tanks to dig them out though.
I just got some from Petsmart, the guy was scooping them out and I asked are you throwing them out? And he was , so I got about 50 MTS for assassin food!
Well seeing you got some lots of people on the forum and other fish forums usually sell them for a few bucks + shipping, or just shipping alone as a roak.