Thanks, Tim. I have had some trouble locating them myself in the past. I have one that was given to me by an instructor. I usually run across 4x5 ones only at the local camera swapmeet. I believe I have seen them at KEH, though, and if I were to dedicate myself to locating them, I'm sure they will turn up right in front of me!
It's funny 2F, I had one.. then when I decided I like shooting these on my rb67, they all of a sudden appeared.