I have searches saved on eBay for all the Xeons as an independent Apple tech - they do crop up. This seller had 5 and went in just over a day. If you can't find anything have a rummage through the dell and hp workstations they may just be listed as six core xeon rather than the W36xx cpu code, there are loads over your side of the pond. With Dell Precision you could always ask for the service tag and look up the spec on their website.
Excellent advice. Thanks so much!
I did find a bunch of X5680 Xeons that are significantly cheaper than the single processor counterpart. I've looked through the forums and it seems like one of those would work as well. Just trying to find out if there's anything I would need to do differently for that chip. I read something about the 2009 models being "lidless" and I'm not too sure what that means. More research.