I'd get on the google and put in the make and model of your grinder and see if there are any parts out there on the interweb.
55-56 Pontiac driver side lug nut? I think it was the driver side that was left-hand thread. One side was.
if your talking about the abrasive wheel retention nut I may have a few of those off of smoked angle grinders.
From the dealer. I got a similar part for my 1989 Makita at Home Depot, they are a Makita dealer. It took 2 or 3 weeks to get it but they got it.
Fastenal also Mc Master Carr in Chicago, order before 3:00 get it next day, no minimum with credit card
Look for a machinery equipment dealer that's local. I've gotten odd ball parts for my sawzall and drills there. I generally buy TWO of anything I had to replace. Bob
http://www.drillspot.com/products/9...3_4-16_left_hand_plain_finish_hex_jam_nut?s=1 http://www.drillspot.com/products/1...r_36915_3_4-10_left_hand_plain_finish_hex_nut