Best way to find and contact absent owners

I've been thinking about this. I thought it would be as easy as a trip to town hall...but not so. They told me they don't know how to pull a list like that, and that most of the time they bill the mtg company direct anyway, so it wouldn't help.
Ok...so I started driving around town looking around...got lost in some endless string of subdivisions.
So is there any other way besides just driving around to find vacant houses?
And once you find them, whats the best way to contact the owners. I was thinking of calling, but with do not call laws, I'm not sure it would be legal or appreciated. I guess a letter then? I dont know what the most successfull way is. Any ideas?