Pin boards at resorts - we found the ones at AoA to only be out certain times, POFQ out all day. Guest Services at POFQ and all the deluxe resorts have pin books you just have to ask to see them. We also found books at alot of deluxe resort gift shops. Guest services near Oscars at DHS has a pin board, not sure about other parks. There were some stores at DTD that had displays of some sort, one place had them on flip flops which I thought was a neat idea. As pp said, many CM's have lanyards but also look for supervisors - they often have hip lanyards that aren't as easy to spot as neck lanyards and they often have better pins. We were told that food service CM's don't trade but otherwise any CM can opt to be supplied with pins for trading, some of my best trades have been with custodial staff, they are overlooked and love to trade / talk to us!
Have fun, its addictive to say the least!