You can try this site:
http://www.pimpadelicwonderland.com/lost.html
Try e-mailing the guy who runs it and see if he has information on the movie. He has it listed as a "lost" movie but the site hasn't been updated in a while so you might get lucky.
Other than that there's always eBay, you can sign up for one of their notification services where they e-mail if it comes up on the auction block.
I've seen this movie mentioned before as an extremely hard movie to find. So you might not have much luck in the usual places. Best thing to do is hit a number of different movie forums and hope someone owns it and is willing to sell you a copy.