In Animal Crossing: Wild World you have to go find Copper. He can be found in the "Main Gate" of your town. If you talk to him you can set up the Wi-Fi connection with him, and he'll tell you your Friend Code.

I'm pretty sure in Pokemon all you have to do is go to a Poke Center, go downstairs, and talk to one of the people there, and they should give you the "Pal Pad" and your own Friend Code.

I can't really help you with "finding someone in particular" because I've never actually been on the Wi-Fi for the DS myself. xD