Unfortunately, I don't think Disney sends out any paper fliers - We pretty much just hear about new pins once they're listed online… and to make it even more difficult, they're spread out on lots of different websites, because they come from lots of different places!
Disneyland and Walt Disney World have their own specific pins, which are sporadically listed here:
http://www.disneyparksmerchandise.com/pins/
Unfortunately, they tend to only list the new releases, so there are probably 100+ pins at either park, at any time, that aren't even listed there. The best way to browser for those pins is on pinpics.com.
The Disney Soda Fountain a.k.a. Ghiradelli Soda Fountain a.k.a. Disney Soda Fountain and Studio Store (It goes by a lot of names) in Hollywood, does release fliers semi-often on their Facebook page:
https://www.facebook.com/pages/Disneys-Soda-Fountain-and-Studio-Store/110503945672358?fref=ts
However, their famous "Pin Trader Delight" pins (PTD's) are released in "surprise" sets of four, so no one really knows what the next set of pins will be until they arrive. And then they stay there until the last pin of the four sells out. (Sometimes it takes weeks; sometimes less than a day! Depending on how busy the shop is, and how popular the characters are at any given moment.)
The DisneyStore.com occasionally offers limited edition pins, too, but they are usually a bit of a surprise, as well. WDI (Walt Disney Imagineering) has BEAUTIFUL pins, but as it's a store especially for cast members, their fliers are top secret to us peasants until the pins are actually released.
Then there's other countries… DLRP (Disneyland Paris) occasionally has online fliers, around once a month, and whenever they come out, someone usually posts it in a new thread on the forum.
Tokyo is a bit harder to follow, but luckily we have a great member on this forum named "dizneydogs" who keeps a very informative thread updated for us here:
http://disneypinforum.com/showthread.php?5321-New-Tokyo-Disney-Pins-***UPDATED***.
And that's all I know - Hope it helped! Great question, and welcome to the forum, Missy. :wavey: