Buyee is mostly used with Mercari https://jp.mercari.com/en

You can use it with Amazon.jp but most of the time Amazon ships directly to everywhere, no proxy needed

In fact you can use it with any japanese store that has a link to a product, the inquiry is free itself and Buyee reports back if they can buy it for you or not

If you use Discord then the Buyee server is very helpful https://discord.com/invite/YRg3DgkBpS