Note that you have to pay for an OpenAudible license to be able to use it with more than a few tracks.
If you can get your activation bytes from one of your DRM-protected files using https://audible-converter.ml, you can then just use ffmpeg (e.g. ffmpeg -activation_bytes XXXXXXXX -i audiobook.aax -c copy audiobook.m4b) or https://github.com/audiamus/AaxAudioConverter to remove the DRM.
Unfortunately this doesn't work for the Japanese store (and a few others) that seem to use a different DRM scheme with a separate key for each file, so you have to use OpenAudible for these.
A rip of this specific limited edition CD, that contains a few bonus tracks that can't be found anywhere else in CD quality.
A PDF of the short-lived Japanese edition of GURPS 4th Edition (specifically Characters and Magic). The books are very hard to find, and usually cost $300-500 when sold online. It seems like no scans were ever made.