Book fairs provide a networking space between authors, publishers, and literary agents. This may be targeted at industry professionals, but it also offers the opportunity to raise awareness of new book releases or special editions. The relationship with authors and publishers will enable you to obtain rare editions before they are sold to the general market.
You can learn about new releases and limited editions at events hosted by book publishers. Through the publishers, you can get a preview of special editions or even pre-order some of the rare books before they are sold to the rest of the world.