Here’s a really nice resource. You can download PDF versions of some rare, out-of-print books (mostly on Okinawan karate) courtesy of the University of Hawaii at Manoa Okinawan Collection. The books are part of an ongoing project by my friend, Charles Goodin, and the Hawaii Karate Museum. Charles collected many, many priceless books related to martial arts and then donated them for proper storage and safekeeping to the University of Hawaii. I was proud to be a very small part in putting together a show that highlighted his donated collection a couple of years ago at the UH’s Hamilton Library.
Besides PDF versions, there are also eVols that you can download. The link to those books are on that page. It’s a great resource.