Well, I have
given up on finding it. I suppose I could wrap the handle of a good oak bokken, and modify it for a fixed tsuba, and buy the saya... but, as someone already posted, what's the point? It's only going to look neat -- it's not in and of itself going to improve any of my techniques.
I thought to pick up a saya for one of my existing bokken, since some of the kata we do requires starting with a "drawing" of the bokken... but my sensei doesn't have one, and hasn't sen the need, so why should I waste the money?
Thanks for all the help, though! Some of those sites, I hadn't found on my own, yet.