If I remember correctly, they are 5-40 threads. Not sure where to get them… maybe PBR

I think 5-40.

I think this is what you are looking for...?? This came from an old wiring harness stack switch I have from a System One.
Screw (resized).jpg

I bought this, definitely worth it: https://www.amazon.com/Screw-Chekr-Thread-Gauge-Checker/dp/B0006NFUJW/ref=sr_1_16

I’d try PBR too.

If it’s 1-1/2” — https://www.mcmaster.com/91792A135/

I believe yours is a fillister head screw.

Measure the diameter of the screw - a #5 screw is 0.125 inches diameter and a #3 is approximately 0.1 inches. I'd guess you need the #3-48 screw, which tend to be used with the smaller 1 3/4" switch blades on the AG and interlock relays. The 3" switch blades (motor and standup switches) tend to use the #5-40.

Screw sizes (resized).jpg

Longest I could find for 3-48 are 1-1/4”.

One suggestion I read (since these screws seem to be used on guitars and some folks are looking for longer) is to use 3-48 threaded rod, cap with an acorn nut secured with Loctite or JB Weld; cut to length.

Hopefully someone has one in their junk box; I saw a reference to this screw in a 1966 Bally parts catalog.

Ive got one to send you if you havnt found something yet.