There's a slot machine and coin-operated show in St. Charles, IL (west of Chicago) on March 30th, 31st, and April 1st. It's called (not so strangely) the The Chicagoland Antique Advertising, Slot Machine and Jukebox Show. Although it's better known as "The Chicagoland Show".

The web site is:

http://www.chicagolandshow.com/

It's twice a year - Once in March/April and again in November. While it's got lots of gameroom, soda fountain, peanut vendors, etc., I go for the slots. It's a good show and only costs $7 to get in for a day. If you're looking for a slot, or to have one repaired, this is the place to go.