It might be tough approaching demo / construction companies and going in and "cherry picking" with little or no compensation to them. Maybe a nominal "finders fee" and some additional personal demo labor thrown in to sweeten the deal could make you their "#1 go to guy" when new projects came up?
It's a shame to see tight grained wood go to waste, not to mention beautiful old fixtures and hardware. I'm sure you've read it, but "Old House Journal" is filled w/ arch salvage ads and maybe you could pick their brain or ask on their forum. Good luck
edited to post link:
http://www.oldhousejournal.com/