This may help (you laugh a little bit.)
"Acquiring Game Rights" by Phil Orbanes; The Games Journal, September 2000.
A final strategy, if all else fails, is to actually republish the game. Doing so will usually flush out the rights owner who will contact you and make demands. You should be prepared for this and set aside at least 5% of all sales for royalty payments when this occurs. There is a risk here because the rights owner may have something else in mind and may seek an injunction. But the risk is worthwhile if you feel the rights owner has disappeared or you feel he or she would be delighted to have some income flow from a game without licensing interest elsewhere.