I don't know of many Australian jewelers besides Holloway Diamonds, owned by Gary Holloway. But I don't know if he is anywhere near you. However, you can absolutely buy a cushion online successfully, you just need to find a vendor that does more business towards cushions than the one you're presently with. Nothing against James Allen, but they're less geared towards fancies, and more towards rounds. They're not the vendor I'd do this particular purchase with being where you're located. In the States, yes, not in Australia.
Good Old Gold and Engagement Rings Direct are two that are well known for excellent cushion selection. GOG is very good with fancies of all kinds, in fact, and does videos for customers, and tons of great images of stones to help with selection. Being half a world away from your vendor, this is crucial. I'd strongly consider contacting one of them for this process. Both should be well versed in working with overseas buyers, I know GOG especially is. If you want a specifically H&A style cushion, GOG or Brian Gavin Diamonds, again both versed in working with overseas and Australian shoppers. Just something to consider before you pay for this one which I see is marked as not available.
Good Old Gold and Engagement Rings Direct are two that are well known for excellent cushion selection. GOG is very good with fancies of all kinds, in fact, and does videos for customers, and tons of great images of stones to help with selection. Being half a world away from your vendor, this is crucial. I'd strongly consider contacting one of them for this process. Both should be well versed in working with overseas buyers, I know GOG especially is. If you want a specifically H&A style cushion, GOG or Brian Gavin Diamonds, again both versed in working with overseas and Australian shoppers. Just something to consider before you pay for this one which I see is marked as not available.