Also, still interested in these figures for purchase. I'd be using them as fodder in various personal custom projects, so condition isn't a big concern:
Hey man - you could check out Dr. Deadman over on the Spawn forums. I know he was selling a TON of casts back in the day, including Endo skulls. Here's a link to that thread in particular:
http://board.spawn.com/forums/showthread.php?t=510397