I bought six of them last year from someone who didn't really know what he had. Paid about $60 apiece. One was used, the others were new. Also saw someone on the forum a few months ago who had several he was planning to sell, but never saw them listed on Ebay. So evidently they're not as rare as you'd think based on the description at Clickykeyboards.
Now Ripster's Industrial SSK, that's rare, as well as his Financial Keycaps SSK.