I have an engine that was converted from a strimmer (I think)

and it had a domed aluminium domed prop nut which has a knackered thread (my fault)

. I have searched the internet but cannot find a similar nut anywhere. It has a hex base and is 28mm across the flats, it is 44mm long and the first 16mm is not threaded then about 20mm of thread. The shaft is 9.4mm diameter but not sure yet what the thread is. Can anyone please point me in the direction of where I might get a replacement?
Thanking you in anticipation
Steve