This might be of interest:http://ci.nii.ac.jp/ja
Academic articles (search for articles with .pdfs and you can download all of them). There is no shortage of articles on Buddhist related subjects.
If you find an author you like, look at their publications. Chances are they might have a work or two. Be aware that academic works in Japan cost an arm and a leg. US$300 and up for a single monograph is the usual price.
Here is a sample article you could download:http://ci.nii.ac.jp/naid/110000042391
If you are in Tokyo or visit there, go outside U of Tokyo's Akamon 赤門 and you'll find Sankibo 山喜房佛書林 bookshop which is a treasure trove of Buddhist academic works.
They have a site you can browse:http://www003.upp.so-net.ne.jp/sankibo/