Thats a tough one to do I imagine.
You could go door to door.
You could ask your freinds to ask around.
You could build the next big thing like a website community localizing all its members or some fandangled database of players and then post ad banners on other websites that say something to the tune of "MEET LOCAL PS3 PLAYERS IN YOUR AREA!"
You could post what city, state, province, country you live in right here in this post.
You could go to your local game shops and ask people there what consoles they play. (thats a good one there!)
I live in Indepence, MO for example. Does anyone want to be my freind. I can be a real bleep if you know what I mean. I live in a dump because I'm poor and I hate rich people because they have it better than me. I'm anti-social, married with one kid and a dog who hates whoever I hate.
SO WHAT DO YA SAY! LOL
I'm 32 almost 33 years of age. I had a young guy move in next door to me last year and he has since moved but I talked to him a few times and found out that he had a ps3. He however did not have internet and did not want it he said. Chances are probably good that you have some neighbors that have ps3's. Theres ways to find them but it requires "YOU" to do more than make a single post on the vast internet.
EDIT: I just want to add that I also shop at Best Buy and I know that theres a employee there that I spoke to that plays ps3 also. And I found that out just by talking about a game I was looking for. It's just that easy.
You could buy a blank T-shirt and iron on paper then print on the paper something saying "I OWN A PS3, IF YOU OWN A PS3 LETS BE FREINDS"
See how many people aproach you and then try to give them a tic tac. If they take the tic tac then you say "Freind request accepted".
put an ad on craigslist or better yet POST your area.
On whatever games you like to play make a new post on these forums someing like "ANyone from the ***** area?" and chances are youll find someone kinda close who will reply.