AMA members get listings for upcoming events in their state; it's usually printed in the Model Aircraft magazine, as well as being on their Events page:
http://www.modelaircraft.org/events/calendar.aspx
Now, granted, all of the ones on the AMA website are AMA sanctioned, so you must be an AMA member to participate, but since most of us are members, it's not really a problem to participate.
Some of the shows have "fly in" or "landing fees", but it's their way of charging non-members to use the field (and sometimes, it's done to supplement the event with a BBQ lunch of burgers & hot dogs).