If using ebay, I've found it's watch and see, it'll show up sooner or later. It can take weeks or months.
You can also try contacting knifeshow dealers, the people that specialize in going about the country selling (and finding goods at a low price to sell at the shows for a profit) older/custom knives.
Some of the sellers on ebay are such people, and I've found more than a few that are trustworthy/good people. It's usually noted what they do in the "me" section.