Hi,
The pins in the series are:
item.2012=The Haunted Mansion (1/9)
item.2013=Fantasyland Castle Retro Pin
item.2014=The Enchanted Tiki Room (3/9)
item.2015=Adventureland Retro Pin
item.2016=
Disneyland (5/9)
item.2017=The Pirates of the Caribbean (6/9)
item.2018=The Matterhorn (7/9)
item.2019=Tomorrowland (8/9)
item.2020=it's a small world (9/9)
You may notice that the Fantasyland Castle Retro Pin and the Adventureland Retro Pin have had the numbers removed. They are indeed 2 and 4 of the series respectively. No one knows why they have renamed these pins.
If you look in It's a Small World Imports, the pin is sold with the number but then mysteriously changes name to the Fantasyland Castle Retro Pin.
All pins in the set are buyable except for Adventureland Retro Pin, which is quest only, the Disneyland (5/9) Pin, which was available at DLR, and the Tomorrowland (8/9) Pin, which was sold during celebration weekend and then given by staff for prizes occasionally. (The Fantasyland Castle pin is quest, but is also buyable)
Hope that helps!