All demolitions have permits that list the owner and contractor and proposed date. Don't expect to find much that way. By the time a place with valuable items is actually scheduled for demolition all the good stuff is sold or stripped. Often the demolition contractor owns the rights to salvage in return for reduced or no cost of demolition. So you could call demolition contractors.
In any event, Most owners and contractors do not want the public rummaging through buildings scheduled for demolition due to liabilty concerns. You might be stuck with a salvage store.