Good morning, son
In twenty years from now
Maybe we'll both sit down and have a few beers
And I can tell you 'bout today
And how I picked you up and everything changed
It was pain
Sunny days and rain
I knew you'd feel the same things...
Ebay is awesome if you can't get to the parks, but i am not sure where you are directing your question. If you are asking about in the parks, i can help you out with DLR. In Disneyland, The Little Green Men Store Command next to BLAb is a great place, as is the Frontierland pin store. In DCA, P.T. Flea Market is the place to be.
The Disney Store also sometimes have good pins to trade too. Look for multiple pin sets...the more pins for the same price the better. When they first started selling pins again, they had a set of Snow White and the 7 Dwarf pins for 14.50! And, occasionally they have sales on the pins, and coupons too!
Also, many of the pins are available at disneyshopping.com
At the DLR at DD, the pin trading store is great. There can be lots of people in mid-afternoon, however. The store does have a large variety of pins and it seems like every time I go there are multiple cast members with large pin bags. Yesterday a CM's bag was filled to the brim with HM (Hidden Mickey, not Haunted Mansion) pins. It was great!
becareful on ebay. some sellers are good and honest but some will sell you all counterfit disney pins. if you find a good ebay seller stick with them. i have one i love but she only occationally sells lots. fairly frequently but i only can get to the parks every few months so it works awsome for me.