You can buy from Amazon JP, but you have to use a VPN and give the address of a hotel or something similar. I know of people who used the address of the Hilton Hotel in Tokyo for instance and it was fine.
You can also use a proxy address service such as Tenso. They will provide you with a virtual Japanese address and you’ll be good to go.
There’s also Kobo Books Japan that doesn’t require the use of a VPN but still requires a Japanese address.
I think Kobo is a better choice, because the DRM is much easier to remove if you want to import these books into Lingq.
Tenso is a parcel forwarding service - you can use it for printed books or other things you can buy from Japan and want to receive in Au or wherever. So provides you an address you would use where you need a Japanese address. How it works is described on their home page - you register and get the JP address for your use.
I don’t live in Japan but I do have a product I bought that includes a Japanese Audio Drama. I was planning on posting it on here later for my private use. If I can send you a private invite for it here I will.
I may not do it in a timely manner and be sure to remind me.