hi
This is going to be the hardest one for you to find.
I know where two or 3 of these are but there are 17 more out there somewhere. they are marked on the back strap with a BP Number.
good hunting.

Pre Model 45 M&P Special 22 Caliber 22 S & W Long rifle Serial Number K359459 Shipped April 13 1957 To Boston Police Dept. Boston, MA. Company shipping records show this Serial Number was shipped with a 6 Inch Barrel, Blue Finish, Magna Stocks with Fixed Sights. Shipment was for 20 Revolvers.

jim