I remember a site that had all sorts of E-MU specific ram somewhere out there. Hmmm. Even low profile 30 pin SIMMS for the ESI series. I was hunting for SIMMS and found some on e-Bay cheap! From that previous site the E-Synth takes 70 ns or faster EDO or non-EDO 72PIN SIMMS, but not ECC RAM.
http://www.msiinc.net/cgi-bin/quikstore.exe?keywords=72pin&category=memory&search=yes
(not me, just a quick search)
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=375783491
The link at the top is a computer parts watchlist that you can search for SIMMS. There are some there for less that $70. Best of luck man.
FP