I hadn't realized quite how many Japanese audiobooks are available in the US Audible. They are a bit of a bear to find, but using either the genre search and limiting to Japanese or doing a search in Japanese (like by publisher 講談社 文藝春秋 新潮社) you will get quite a list.
I haven't yet figured out why I can't purchase all the titles listed (as in no price or purchase button) but I have a call into Audible to see if they can explain it to me.
There is overlap with audiobook.jp, which is no surprise. Try both and choose whichever works for you.