Contemporary- Fantasia Gifts - just ask at the register for the trading board.
Contemporary Market - far end of the 4th floor concourse - have a hat with pins
Did not do this but was told at the AKL that there is supposedly a gentleman King Pin that comes Monday - Friday at about 2pm. Check in the Gift shop in Jambo
Most concierge desks have a book or bag.
Mouse Gears has a board that comes out but only at certain times
Pin Traders in Disney Springs - cast members and then a some point during the day - completely random and not announces they do have a pin trading opportunity - in all our years I have only seen this open once.
The Guest relations desks in all the parks have pins but you do have to wait in line which can be considerably long
MK - Frontierland Trading Post - have a board at the register
TTC - the gift shop has a board
EPCOT: stroller rental used to have one - didn't check it this time
DHS: Guest relations and Package pickup
AK: Not sure they have the tree anymore -that was before they redid the store but can ask at the register near where they sell the pins in
AK: The gift shop before you enter the park by rainforest cafe had a vest or a board
Just keep an eye out to all cast members with Lanyards