I have 1954 M21. Parts book doesn't show the clips and where I've been ordering parts said they wouldn't have it if not in parts book. This would be what holds the headlight in the in the chrome piece then it all goes in the bucket. Need to know where to get it and part# to ask for. I think there should be a gasket also. Also need glass and bezel for speedometer and the big rubber that helps hold it in cowl.
They are called W clips and they are nearly all the same even if they are for a Japanese bike so if you order some from eBay they will probably fit ok. The seal is a cork one which I doubt you'd find easily, you could cut one from a strip of cork gasket material and just glue the ends together likewise you could do the same with some soft rubber material.
The speedo glass can be easily obtained from a glass merchant, they can cut you a circle for a couple of pounds.
No cork seal in the headlamp of a 1954 M21..The pre focus reflector/glass assembly just 'clips' directly to the headlamp rim using the 'W' clips Dave described...
The 'flanged' type speedo bezel used with the nacelle rubber should be available from any speedo restorer...
For the rubber itself try C&D Autos, Kidderminster Motorcycles, Draganfly Motorcycles etc. ...Ian