They are harder to get than Model M, aren't they?
Yep they are harder to get, and even harder to get them NIB like mine. Until Cindy made these available the prices for these "little" boards were big. You could go over to Deskthority and watch the marketplace, for time to time elecplus finds some of these boards and if you are quick enough you can get one.
For the NIB ones the price was 150$ plus shipping to Europe, and that is more than a fair price for a NIB SSK. I think there is also a list.
A few days ago 3 SSK were made available but got sold really quick.
Few months ago she had a lot of model F boards beamspring and SSK available, you could get your hands on a used SSK for only 25$ back then, so it's a matter of following the threads and being in the right place at the right moment