Also note the stores do not want to sell him a latching switch and FOR GOOD REASON...
Lets say the OP has his 6 y.o. grandson in the shop with him...If the foot pedal has a momentary switch on it, when Grandpa lifts his foot from the pedal to go get more stock, the grinder dies immediately...
No! Give it a rest.
Have you EVER seen a grinder with foot pedal momentary switch? I can say for sure that I have not. Every bench/pedestal grinder I've seen before had some sort of toggle, pushbutton, paddle, or lever switch arrangement that was not momentary. There is simply NO advantage to a momentary switch on a bench/pedestal grinder. Heck, momentary switches are not even the norm on hand-held grinders (and I've made comments before as to how I feel that they detract from, rather than add to overall safety).
I've never seen a grinder with a safety brake, so no, lifting a foot from a "deadman" pedal is not going to stop a grinder immediately. It'll keep spinning with all of its potential energy for quite some time.
Regardless, OSHA does not have any requirements for momentary switches on grinders for good reason. The biggest danger from grinders is a fracturing wheel (something that is generally preventable). The next biggest is entanglement (which is also not an issue if proper shop safety regarding hair/clothing is followed). Then you've got eye safety. Grinders are simply not the death machines you make them out to be.
I distinctly remember being a 6 year old in a shop with a 24" radial arm saw that took several minutes to spin down after being turned off. I knew well enough to stand a safe radius away (well more than 10'), and if I didn't, there's no way I would have been allowed in the shop.