Check out the classifieds at Ruger Forum or just post a wanted ad there for the .22LR cylinder. You'd be surprised at how fast you can sometimes find stuff there.
The rear sight on my KP89DC broke a while ago, and it was supposed to be replaced under warranty (pistol was only a couple of months old, and the break was probably a freak casting issue). Location Snapshots (Ruger Canadian supplier) told the guys at Reliable (where I buy my guns) that there was a "backorder" on parts from the Ruger factory. After waiting for months on end with no ETA for the part, I got frustrated and bought one off of someone from Ruger Forum. In my frustration, I also called Ruger directly, and they were "surprised" that I was being told this as there is no such thing as "backorder" of parts as they have lots. Ruger said they will sort out the "backorder" issue with the supplier, and promised to expedite a rear sight for me. My new rear sight arrived in the mail yesterday, a couple of weeks after speaking directly with the factory.
I love Rugers, have several of them...but dealing with their Canadian supplier for service has left a sour taste in my mouth. For the .30-06 that I'm buying in the near future, I'm strongly leaning towards Savage instead of the M77 because of this experience.
Back on topic...that's why I'm recommending you either contact Ruger directly, or the folks at Ruger Forum (probably the cheapest route too) instead of the Canadian supplier.