Not being able to remember this bugged me enough to look it up. Thanks. lol
Here's your two options I know of; aimtech and B-square.

Aimtech Black Mount For Smith & Wesson 422/622/2206 APM11 FREE S&H APM11. Aimtech Riflescope Mounts, Rings & Bases.

http://www.hunt101.com/data/500/2206_Red_Dot.jpg

It may take some patience and perseverance to find a B-square. I don't think they've been made for a while, but they come up every so often. Good Luck