Bryce, you probably saw my thread on RFF, but I just grabbed what I think was the last one at B&H for cheap. Actually had it in my cart, took an overnight to think about it, and it had disappeared in the morning and was showing out-of-stock. The next day, however, there was one in stock again somewhat miraculously, so I jumped on it.
Originally Posted by Leigh Youdale
There was a sub-$400 one on Ebay (new) that seems to have disappeared, so PhotoVillage at $400+ seems like your only option for a new one, and not many seem to come up used at this point. CameraQuest has them for $599 in both black and silver, and seem like the best place for product support (and sincerity/enthusiasm; alas, I went for price, and took a risk on support.)
You might get best bang-for-the buck looking at a Canon leica threadmount lens, or an older Elmar 2.8 in good shape.
Maybe try emailing Sherry Krauter (google her site) and see what she has in stock in threadmount. She's a noted repair tech who sometimes has a small stock of lenses. Her online inventory is very out-of-date, however.