When you get to the part of the game where the Higsby guy from the school incident has a business as a chip salesman (in front of the gates of the school), go inside and save your game next to the chip trading machines (the ones that resemble candy or mini-toy dispensers in real stores). You can now freely trade 3 or 10 chips for another one, depending on which machine you use. If you do not get a chip you want, turn off the game, turn it back on, and resume from your save. Repeat the chip trade until you get the one you want, or get a rare one.

Stand in front of the 10 chip machine and save the game. Continue using chips until you get the desired chip. If you do not get it, turn the game off and restart. Keep repeating this until you get what you are looking for.