Where did you find a replacement for the JM spinner???

Anything that has enough force to flatten the metal. I'd use a Dake arbor press...but you could use just about any hydraulic press, too. If you are looking for a hand held tool.....not very likely. There probably is one but they won't be common and won't be cheap. It'd be a purpose-built tool and would need to be fairly stout to produce the kind of force you need.

Those are a bitch to crimp. Here's what ended up doing.

https://pinside.com/pinball/forum/topic/how-do-you-guys-press-smash-this-pin#post-4190885

Not a lot of stress/strain. Use a small washer and epoxy it on the shaft. Epoxy on the outside shaft so epoxy doesn't interfere with plastic washer.. Clean first with solvent. Another easy option is to go to your local hobby shop and get a model airplane control rod stopper.
The rod is hardened and is difficult to work with.

Is that even necessary? It's physically impossible for that to just pop out during gameplay, right?

how's the next guy supposed to get that off?