I'm looking for just the same thing.
I hate junk faxes, but I've figured out a way to get some satisfaction.
Currently there is no law that says (where I live) that I cannot program a computer to call numbers looking for fax machines. I think there's a restriction in that it cannot call in order, but randomizing a list is trivial.
What I propose to do is as follows:
a) find fax numbers; b) when a fax number is found, send a fax saying: i. hello fax machine, I've found you. ii. I'm making a list of fax numbers, and you are number ; iii. I am selling my list to companies who wish to do mass faxings; iv. you can buy my list for $x; v. you can have your number removed from my list for $y; vi. if you, like me, hate junk faxes: 1. there's no law aginst it right now; 2. if you, like me, would like a law aganst it, contact one (list of local legistlators); 3. in the meantime, I'm happy making money.
Think I'll start with the prefixes that cover the local government offices first ...