OK, got my order in. Forum to the rescue again. I expected a 'magic formula' but I'd rather order a bottle.
No, Micro-Mark is not gone, but it's not promising either. No more mailed catalogs. Huge list of closeouts. The website isn't exactly excellent for search and display. Some of the supplies I counted on like tie stain, some paints, 10-1 molding rubber, etc. - a lot of the 'Micro-Mark' branded stuff, were discontinued without notice. The molding rubber in particular was excellent and they had said it would be restocked, now discontinued. 
I've literally made hundreds of molds using that stuff and it's really held up.
You're right - I have not received their printed catalog for some time (or looked at their website).
As for their casting materials, I believe they were just relabeled/repackaged items from SmoothOn.
https://www.smooth-on.com/Alumilite also supplies wide range of resin casting materials.
https://alumilite.com/Both companies sell direct and have sample sizes available (perfect for hobbyists). I have dealt directly with both and I prefer SmoothOn products, but it has been a while since I tried Alumilite and they seem to have greatly expanded their product line.
Also, not just hobby shops carry those products. Theatrical supply shops and craft stores might stock RTV and Urethane resins. SmoothOn also has a local distributor finder on their website.
