I am not sure what company you used for your reservations, but we have used Costco and GetAwayToday in the past. Both packages came with a lanyard and pin set for each parkhopper purchased. It was one lanyard (with logo of CostcoTravel and GAT) with a single pin for each person.
At the time I was the only one in the family that was intrested in pin trading. I took all of our pins (so I had 4) and put it on a lanyard. That is how I started trading. I made it into a starter set.
Since that time, my DH and DS have caught the pin trading bug and we all do it now.
Have fun!