I just happened to talk to Tamron this morning, about my RF645 that could use a bit of adjustment to the frame spacing.
The woman who answered the phone was very friendly and helpful. She said that as of October, 2011, they could no longer do any servicing that needed replacement parts. But they were continuing to do other kinds of service. Apparently there is one guy who is working on the cameras, and that I should expect a ~2 week turnaround for most things, and that service fees started at $90. I asked specifically about repairing loose winders (a common issue on these cameras), and she said that doesn't always need new parts, so it may still be possible to get that fixed.
I'm half-seriously looking for a second body, primarily so I can have two kinds of film loaded while traveling, and then swap lenses between them, but also as a backup so I can send my current one in for service. They seem to be coming up on eBay and KEH fairly regularly, so I wouldn't say they're *too* rare.
--John