Graf water barrel tap

3 years ago I took up an offer through the local council and ordered a water barrel from Blackwater.

After a long wait a Graf 200 litre barrel arrived, but the tap that came with it was a Sankey type and would not fit. Eventually the right tap was received.
(For information if you are unaware, the Graf has a male spigot moulded on and the tap has a captive pressure nut to secure it.)

The problem now is that the locking ring has split and the tap is therefore useless.

I have done extensive searches but have been unable to locate a supplier for a replacement.

Has anyone come across this problem and managed to find a replacement?