I came across this on the B&H website, and ordered it. It showed up, and much to my surprise, the female end is only 3/8. Which won't help me much unless I saw the top of my new stand off.
I'm going to call B&H and politely complain on Monday when they open again, but in the meantime I called a handful of local "photo & video" and "sound & lighting" and "professional music" stores, and none of them have anything that can help. Actually, that's not exactly true; one store had a $40 adapter with a spring-loaded sheath for attaching to boom poles or something that would work. I'd prefer to spend quite a bit less than $40, if I can avoid it.
So, since I appear to be at a loss, and at this point I'm a little over a week away from a bunch of shows that I wanted to try my new mics out at. Has anyone out there dealt with this, or know of someone who sells an adapter like the one I'm looking for? It seems to me that a "5/8 stud to 3/8-16 threaded male" would be more common than 5/8 stud to 5/8-27 threaded; I'll take either, but I seem to be able to locate neither. Any suggestions?