Uptownbabe is pretty much dead on... On our visit to WDW, we were blown away on how many pins there were to trade among cast members, pin boards, guest services books... Not here unfortunately... Heres our breakdown as I know it...
Best time to trade with cast members is early mornings and early evening before parade on Main Street.
Pin boards are picked to death most of the time, but they are located at pin traders in frontier land, Disney store on Main Street, a small book in Tomorrowland giftshop at exit of Star Tours... DCA has one at end of Hollywood Blvd. and one in giftshop accross from Little Mermaid ride.
Pin traders are as mentioned above and they do still meet at the end of Main Street on Sundays, but the tables at Frontierland is the best location.
Best days are... of course Thursdays for new pin releases and Sundays, followed by Fri, Sat, & Mon... Tues and Wed are pretty quiet...
Let me know when you visit, I love to trade and I am at the park often...