>>773399A Triple Double?!!!?!!
My humble advice - just drive around cities nearby that are older looking or around cities that had industrial companies in the past. You should generally be able to tell by your city if there's cool abandoned places to check out.
I know this sounds useless, but the point is if your city is not sufficiently "old," rural, or industrial enough any place you do find will either be monitored by security or filled with hobos.