There are hundreds of specialty stamp societies and study groups all over the World, including many that are located within the United States.
There is a specialty society for just about anything that is collectible, whether it be for a specific country, or a special type of stamp, such as coils or booklets. There are also societies that specialize in related collectibles, such as cinderellas, revenue stamps, thematic stamps, postcards, etc.
Almost all of them publish their own monthly journals, which contain information focusing on their particular specialty. Many of these societies also have sales circuits for members, websites with specialty information, and in some cases, they also sponsor awards in their specialty category at shows and exhibitions.
In the past, I have been a member of the U.S. Philatelic Classics Society and the American Topical Association, and I am currently a member of the American Helvetia Philatelic Society. If you are specializing in a certain area, being a member of a specialty society or study group is an invaluable way of increasing your knowledge of your specialty and of interacting with other specialists in your area of interest.
first link section below is to the directory of specialty societies on the A.P.S.
website. Membership information and usually website addresses are
listed for each of the societies.
The second link section below contains banner links to specific specialty philatelic societies. The first of these is the AHPS. Since joining this society in 2010, I have found it to be very useful for my own Switzerland collecting specialty. Their bi-monthly journal, TELL, is a magnificent source of information on various Swiss specialty areas. I have even added specialty areas to my own collection, based on some of the articles I have read in their journal.
There are societies, based in other countries, that may not have affiliation with the A.P.S. For those, you can find them, by searching the Internet.