If you’re in NSW (?)…..then Cl.98-1(a) of the NSW Strata Schemes Management Act (1996) states that the Strata Roll must include “the Owner’s Name and an Australian address (my emphasis) for service of notices or the name of the Owner’s Agent appointed in accordance with Part 3 of Chapter 4 and the Agent’s Australian address for service of notices”.
So as the Unit is under the management of a local Agent, your Owners Corporation (O/C) should write to its overseas Owner to request that, in accordance with the (State) Law, they nominate that person as their Agent for the service of notices.
If that nomination is not made, then I think that your O/C could obtain a Court Order allowing it to substitute the Owner’s details with those of their Australian Agent, and then if payment is still not made your O/C should be able to take debt recovery proceedings against that Agent, or even garnishee the rent proceeds.
I imagine that with the increasing numbers of overseas (investor) Owners of Strata properties, if there’s not an easier way to overcome the problems you raise, then there should be!