A big thank you to Tim in the spares dept at Shimano Australia, who managed for find an identical part on a discontinued Twinpower 6000FA (which I didn't realise had even been released in Australia). For a very reasonable cost, the part is now on its way to a relative's address in Australia.
Great service - I don't live in Oz, and bought a reel that isn't even available there, and in a matter of a few hours he had it sorted.
Thanks to Luke for the suggestion and to other posters for their advice.
Cheers, Ian