North Leicester Motorcycles is pretty much the only place you can get some of the more obscure parts for old Morini bikes and I went there for the first time last week.
It reminded me of an old ironmongers shop, the like of which you dont get anymore with almost any part you care to name in stock.
I came back with a centrestand bolt and the hollow spacer it goes through, the old one of which I had to blowtorch off the frame, and some assorted gaskets and a new set of half rings- I was initially surprised to discover there are three different shapes of these, fortunately I got the correct ones as I forgot to take any samples with me.
I was initially disappointed to find the new half rings didn't seat onto the new castle nuts, but while looking at them all it struck me the ones that I removed from the from outlet was oxidised red- rust = steel and therefore too hard to easily file to fit.  The new ones didn't seem as heavy but were hard, after checking with a magnet, the smaller old set and the new set were not steel and five minutes of trimming with a file and the new half rings nested comfortably into the new exhaust nuts.

The two nuts in the foreground are the ones that were on the bike, the half rings were on the front outlet held by the nut on the right, they nest in that one easily, they dont fit into the other one or the new ones at the back.
The new half rings(at the rear right) fitted after a bit of trimming.