Buying Video Game Soundtrack CDs?

I have only purchased a handful of video game soundtracks which I adore such as Shadow of the Colossus, The Last of Us, Voodoo Vince, Journey (digital) and Transistor (digital).

I live in Australia, and the only stores I’ve seen physical copies of soundtracks is at JB Hifi.
I’m currently looking for a few soundtracks such as Gravity Daze, Echochrome, the Katamari series, and rarer/older ones such as Ridge Racer Type 4.
Many places I’ve looked including online stores such as Play Asia are out of print, out of stock or are just ridiculously expensive for a single CD.

I’m wondering if there’s a physical store over here in Australia or an online store which you might recommend to find some video game soundtracks at a reasonable price.
Perhaps a store in Japan/elsewhere which is known for exporting CDs worldwide?

Additionally, I have a friend who will be travelling to Japan soon. Are there any stores there which you would recommend I could find any of these soundtracks easily?

Thanks!
-Craig