Most any hardware store should carry those switches. Here's one example: http://www.acehardware.com/product/index.jsp?productId=29108166
40 years of service is admirable.
Are you still running the original 40 year old magnetic ballasts?
Members with electronic ones that **** out after 2 years might be jealous.
Are you considering upgrading to LED? (probably not)
Do you have a good supply of t12 tubes? I have heard that they are no longer being manufactured.