I was planning on just making some out of metal, but my primary problem is that the window channel has been ripped or cut off, so there's nothing to guide the window. Putting metal tabs on would just make the window shatter.

There isn't really much to those plastic pieces ... they could probably be made out of a good piece 1/2" PVC stock with a dremel if you take your time. I was thinking of trying that, too. They don't need to be exact - just close enough to fill in the rest with adhesive. Really they don't need to be as fancy as they are. You really just need a slot in a piece of 1/2" plastic with a hole drilled for the bolt. In fact, now that I think about it, the replacements could be much bigger so they can handle more stress ... hmm.

http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7539628733

I might give that a try. Heck, I could probably cut the slot nicely with the tablesaw (very carefully, of course).