The very first Kingdom Hearts trading pin was sold at the Sci-Fi Academy event that took place in summer of 2011.
Sci-Fi Academy - Kingdom Hearts - Mickey, Donald, and Goofy
Unfortunately, only 500 of these were ever made so good luck finding one for yourself.
Second KH pin ever released is an Organization XIII Mickey.
Kingdom Hearts - Mickey Mouse
This one came out in summer of 2012 and it's an open edition pin. However it's been appearing on and off in pin stores around the park so if you come across it, snatch it up quick.
Any chance of a Keyblade collection? Only time will tell.