ebay - Within a short period of time ebay has become the major marketplace for vintage crate labels. Quite a lot of material, and sometimes good deals, as long as you can find your way through the maze.

http://www.fruitcratelabels.com/fruitcratelabels/ - Pat Jacobsen has to be considered the obsessive label collector. He has put in over 20 years of relentless searching, has published books and built probably the largest or one of the largest label collections covering any type of label that was put on a fruit box, or can. A good source for information and rare material.

The Citrus Label Society  - The website home of the Citrus Label Society.  This is a club that meets on a monthly basis in the Southern California area.  If you are looking for information on the California citrus industry, or a specific rare Citrus label, these meeting are the place to find them. They also put out a newsletter.

Jack Gaudette - 1-509-575-0393.  Jack isn't hooked up to the internet yet, so you'll have to call him.  Jack puts on the annual Yakima swap meet every May.  He also has a good selection of Northwest labels.