You can get them anywhere that sells fishing bait (cause that's what they are ). Certain gas stations or Wal-Mart usually have them in a fridge somewhere.
It'll take them a month or two to get established, but after that they multiply fairly steadily. They're not prolific or anything, but if you're only feeding one tank, it should be more than enough.
Nope, no smell to it whatsoever. They're extremely easy to maintain, just toss some old veggies or whatever in for them every few days and keep the dirt slightly damp.
I would be happy to sell any that breed. I may have to create a species tank since I can only find ~5 of the 20 I bought. All small fish in the tank so not sure what is going on.