The author will be publishing a volume 4 within the next several months (2018) and if that is successful will publish updated volumes 1,2 and 3. The interest in these books is a niche group and as such he has to publish this on his own. He is looking for either pre-orders or help in crowd funding. He has also promised not to ask for any money until he has reached the required amount of 125 orders. Also crowd funders will get their names mentioned in the book (probably like a special thanks etc..).
I think it would be well worth it to support him since if volume 4 is successful then he can print the updated versions of volumes 1- 3 which would be more affordable than the out of print originals if you can find them at all.
As a disclaimer I have no financial interests at all in this, just helping him get the news out so hopefully he can get the books published. Here is the link to his site:
http://www.bergstrombooks.elknet.pl/bc-rs/