Just surfing around on utube and looking at random Matchless videos it appears that quite a few different models has those badges fitted , Here's a G45 that's also sporting the empty cast in ring as Rohan pointed out .
The winged M tank badge was introduced on the 1938 range and the small round winged M tank badge on the 1952 range. Various engines had an embossed version of the round badge on the outer timing case from 1938 on.
Thank you gentlemen, much appreciated. I had previously searched for images, but never found anything close. With the help of your feedback I did another search on eBay and there is an expired listing for one. It was described as an engine badge and seller notes it is approximately 31 mm in diameter. Now I just need a Matchless to mount it on.