Have you considered putting it up on eBay? Other than that, why not see if you can place a "for sale to serious buyers" notice in a collector's magazine?
Are you familiar with www.thediecastmagazine.com? It might be a good place to start.
Other people asked questions on similar topics, check out the answers they received:
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them