I bought my pins for my group from cheappins.com. I bought 100 pins that we split among 5 people. We ended up paying $180 total, which brought it down to about $1.80 a pin, much cheaper than buying them at Disney. All the pins were tradable. We didn't really care that the pins were old, since we traded them all away anyways!
It took about a week after buying the pins online for me to receive them. It really was so much easier and cheaper. Plus, you didn't have to worry about trading a pin that you actually liked!