Find comps on:
eBay
Etsy
Charish
One Kings Lane
1stdibs
or
Search back catalogs of design auctions at Skinner, Wright etc
or
subscribe to worthpoint perhaps
or
if it is indeed very valuable, pay for an appraisal at a reputable auction house that specializes in modern/ MCM design.
lots and lots of resources out there.
If you need any help, please contact us at – info@designaddict.com