Actually, I got it from some guy who was giving an old Raleigh frame away. It's a rusty, old converted three-speed that had these crusty wheels on them. HE found it on the street--said it sat in front of his house for months locked up, and he finally took a saw to the chain and brought it inside. He wanted to fix it up, but never got around to it, passed it onto me.
The thing is really thrashed--doesn't look to me like it's stolen or anything, and he wasn't selling the thing. I didn't pilfer it myself, also.
I originally planned on building this up and making a fg, but I got stuck removing one of the cottered cranks, and I realized from reading Sheldon Brown's website that the BB was going to be a PIA to convert, also. But the wheels have been sitting around my house while I learned more and more about this stuff, and this morning, I was looking at the rear wheel in bed and realized there was a pretty useable freewheel sitting there under my nose this whole time.
I'm happy to buy a tool instead of a part and tool anyday. Thanks for the info, all.