I broke down and paid $35 for one at Guitar Center. What the heck, I got the mic for free. Anyway, GC had to special order it and Sennheiser had messed up the order, which I found out when the store called me in. At this point I had waited a couple of weeks and found myself in the store looking at another wait. Peering in the display case, I said to the sales guy, "Why don't you just give me the clip on that one right there?" He said he could not, despite the fact that I paid for one and they called me into the store for nothing. I was pretty torqued at this point and complained to the manager. I was not leaving without it. He took care of it.
I wish I had thought of Han's suggestion, because I could have saved a few bucks and I have a couple of broken 57 clips, not to mention that the 421 hits the deck often, due to the fact that the little button on the clip releases so easily.