From what I understand, they're hard to find, and expensive when you do find one. I'd love to find one of the later threadless styled ones. I still have my arms and end bolts. I had one of the older sets, that used a threaded spindle, sort of like a one piece crank.

The only place I've ever seen selling a Black Widow spindle, is Porkchop BMX, but what they have is one of the square taper end spindles, for the Black Widow Lites, or whatever they called the kids' cranks.