For those around the San Francisco area, you might want to check out the Emeryville Vintage Synthesizer Museum:

https://www.kqed.org/arts/11260092/at-emeryvilles-vintage-sy...

http://vintagesynthmuseum.com/VSM_Home.html

https://www.facebook.com/vintagesynthmuseum

(I don't see a Mellotron listed, but the others look fun.)