Can't help you with a list of frequency's Matt - the airline fellas may have a better idea of which ones are the best or you could try the air services Australia frequency management fellows Can't recall the exact name of the department but one contact there is Bruce Bilton
[email protected]
Also have you considered hiring a sat phone in Lu of hf, could be a more reliable option but not sure if the regs allow them as a replacement for hf. Some one in the prune brains trust may be able to help us there.