Hi Brett,
I would measure up the existing coupling and check with UK suppliers to see if they are the same as the later couplings that are being sold. There are a number of UK mower parts retailers that appear to have stock.
Alternatively, you could contact the Australian Allett distributor to see if they can assist with details and if they have any stock here (Allett acquired all of the Atco designs, tooling etc and now produce them under their brand).
Kind regards,
Sir Chook
