On-line? I doubt it. I can recall most of the "moves". It's been a VERY volatile seat since it's inception in the early 80's.
I notice the price collapse while volume going up in Seats vs. Volume chart around 2000-2001. Probably related to decimals/less profit era.
No. Futures were not subject to decimalization. The break in seats was caused by the advent of electronic trading. Prior to the Chicago exchanges evolving to "for profit" status, the precursor to being publicly traded, the value of memberships was directly tied to pit traded volume.
Call the membership office and ask for the file showing all IDEM seat pricing. They will send you a PDF (I think) of all sales going back farther than you care to know. If you run into trouble, ask for Maria Fritz at 312-435-3485 or Joyce at 312-435-3460. Good luck.