Yo @raymp. I posted this list of VDSL Modem/Router yesterday. This might help you finding a modem/router.
Oops, I just realized that this post only includes modem/router for FTTN/FTTB. So it doesn't have HFC routers.
I tried to search some NBN router compatibility unfortunately it leads me to this thread.
Anyway, if you're planning to use a different router for your TPG-HFC be aware that TPG VOIP feature won't work as I believe it's only available when you use their supplied router. (It applies to all their NBN service)