You may have stuck yourself into a corner with this one. Not even remotes.com appears to have a pre-programmed remote (though you could call and ask them). Best I can see is that there is a Lexicon MC-12b on ebay *for parts or repair* that is listed for $350 or best offer plus $158 shipping. This has the remote and manual. Obviously, it is another several hundred dollars, but it may be your best bet unless some other Lexicon expert responds here.
Lexicon MC-12
I picked this up at a bargain price- I realize it is long in the tooth but appears very well made. It powers up and runs diagnostics just fine. The issue is I cannot figure out how to use it :-( Possibly a remote is required- which I do not have. Must it be connected to a monitor for OSD or can it be run from the front panel? I hooked it to an amp and a cd player, but I may not have it hooked up corectly. Any help appreciated. Thanks.