Do you have any pins yet? If not they can be found everywhere at the parks. For me it works two ways, I buy ones from the store that I like an appeal to me e.x. Nerds, cruise line, wall-e, and funky Mickey heads (patterns and such). The second part is sometimes I can fid pins on sale at outlets or get deals online when dis store has sale going on and I usually just grab whatever and take with me to parks. Once you have ones you want to trade, go up to cm's with a lanyard and ask if you can take a look at what they have. I don't buy any off eBay bc theres too much risk of scrappers, or knock offs.
Now. I have a friend who pretty much only collects limited edition ones and limited holiday ones like Christmas and leap year 2012 or last year was earth day pin.
Hope that what you were looking for!