I would suggest following Van Eaton Galleries on social media or signing up for their e-mail newsletter. They hold major Disney memorabilia auctions about once a year and you can watch live and bid online. They are SO fun! Some of the items are very expensive, but I've been able to snag some things like an original etching that was used for EP merchandise the year it opened, opening and pre-opening brochures, items from the '64-'65 World's Fair Pepsi/small world pavilion, etc. They just recently auctioned off the original map of
Disneyland that Herb Ryman drew so Walt Disney could pitch the park to investors. It was amazing to watch! I've also found some good stuff on ebay!