I know this is a very important thing for several DIS brides, so DH and I went on a pin scavenger hunt on our last day when we had to do several stops at different resorts before leaving.
We found the Just Married pins readily available and tons of them at that at:
Polynesian, Wilderness Lodge and Animal Kingdom Lodge (Main concierge desk, the top concierge desk just had Happily Ever After ones).
Grand Floridian didn't have any (they would obviously run out faster), MK didn't have any either. Didn't have time to check other parks.