Wow . . . a Thunderchief! I don't believe I have ever seen one in captivity!!
The only reference I have to this machine is an advertisement which I found last year:
The ad mentions a 'Willow Enterprises' in Glen Burnie, MD. Bear in mind that this ad is probably 50 years old.
Nevertheless, if you google "Willow Enterprises Glen Burnie" you'll find a trucking company located down the road with the same telephone number (Willow Enterprises LTD, 325 Roesler Road, Glen Burnie, MD 21060, telephone 410 768-3400)! A dead-end, perhaps, but maybe someone there knows what happened to the 'slot side' of the business.
If you live in the midwest you might consider attending Chicagoland, the semi-annual coin-op show next month in Chicago. You might just find the parts you're looking for!
Welcome to the forum!