I'm looking for a bit of advice. I have a high end Scan built design machine that I moved on from last year.3990x Threadripper which is an absolute beast for rendering and video work. 256GB corsair vengeance DDR4 ram. 2x2TB NVMe M.2 drives which is great for OS & programs on 1 and cache + data on other with a 16TB seagate…
Overclockers forums maybe, or Facebook groups for specialist tools e.g. Houdini Artists would be my suggestion. I doubt you'll have much luck on Facebook marketplace for such a powerful machine.