These are the MD20 drums that fit the Saiga-12 shotgun. They hold 20 rounds.
These drums are newly listed on GunBroker and have no reserve.
There are 68 of them available.
They are starting at a penny!
GunBroker.com Auctions by MDARMS.COM
If you want a 20 round drum for your Saiga 12, I'd suggest you have a look.