the DIS collector board. Also the DIS Shop. dizpins.com, eBay collectibles (disneyana), the official disney pin trading site at disney.com or pinpics.com. There are a few other sites and the folks on the collectors board will be glad to help.
One other source to check is disneyauctions.com (included the link that got me there.) These pins are limited edition (i.e. more expensive) direct from Disney. Most of these pins are large and of nice quality. Often protypes are available. Thought you might want to take a look and see if this is the type pin you are interested in. Have loads of fun with your new hobby--it's addictive!
The kids and I started 2 Disney trips ago. My DD collects all Pooh related. I collect black/white Mickey and Walt pins. DS likes to get his favorite rides. I think it's fun to concentrate on one subject. We saw a lady in the park that had on a sleeveless denim vest with all Tink pins and a baseball hat decorated with T-I-N-K. It was adorable, I bet she starts lots of conversations. My DD especially likes the Santa Poohs from different countries.