I've gone to quite a few and bought stuff over the years, but I just got lucky and either saw the ad in the paper or a bulletin pinned up at the supply house.
The auction companies send us information on up comming sales just about every month, the mailing info has out state license number on it, so they must get the mailer info from the state license directory.
Contact local auctioneers as well, ask to be put on their mailing list for those types of auctions.
Many auctioneers will scour yellow pages & newspaper ads for ECs to send flyers to about upcoming auctions as the more ECs that show up, the higher the prices will go.