Originally Posted by Sarcophilus Harrisii
nobbysparrow can probably supply you with one if you're actively seeking to purchase another (you did mention Micro-Tools being out of stock). Personally I'd prefer to buy from him. Micro-Tools are great, when they send you the correct item, but I've had more than one issue with that when ordering items from them. Take a look at his eBay listings.
Good tip! I checked eBay and found this: https://www.ebay.com/itm/303211786390
It specifies that it's for an M2 or M3, but surely it's the same for the MP? I messaged him to ask and he said he's not sure as he's never tried with an MP. I can't recall if there's some odd little tiny difference in the size of the retaining washer or something, but if anyone is 100% sure, would be great if you could chime in.
15.8mm works out to 0.622", which sounds pretty damn close!