The website boasts a complete list of pins, and there are well over 50 (I counted 64, total). While the core set is available on the Penny Arcade store, some of them are only purchasable exclusively at certain PAX Events, like PAX Prime or PAX AU. Some are limited editions that are only received through special rewards, like the PA Kickstarter.
You can head over now to check out the trading rules, pin sets and forums. Don’t forget that there’s a special coupon on Gabe’s Twitter feed!