My sense is that a lot of the studios in major metropolitan areas were and perhaps still are serviced directly by Sinar reps who visited the studios, so there was less reason to sell through retailers. High-end digital for studios tends to work in the same way or only through select outlets--you don't really see it at B&H, but maybe Calumet or Fotocare.

If you want very clean equipment, look on eBay for a seller named "apogeebee." His prices are on the high side for eBay, but the equipment is well selected and represented honestly. He's a studio photographer named George Brown, who made a side business of buying and selling Sinar gear. I met him once when we each bought similar cameras from the same studio, and he accidentally got mine, and I got his, so we switched, and it seemed like he knew the system very well.