the answer is that they do jobs
A philographist collects autographs
If there is anything a collector like to do besides collect is talk about their collection. Many collectors gather in specialty forums to discuss their hobby. Find a forum dedicated to the sport you are looking for and a discussion about autograph collecting will be posted. Just about any auction site will have a large community of autograph collectors looking to buy memorabilia. Do a search on eBay and you will find thousand of listings with plenty of collectors bidding. Sports memorabilia shows will also be a magnet for autograph collectors.