I have recently acquired several collections of books on pipe organs and their history. Most of the books are in excellent condition and quite a few are hard to find. The first catalogue out with some of this new stock is No VI (August 2018) which lists 77 separate titles. A PDF file of the catalogue is available
here.
Further catalogues will come out shortly.
If there is any particular book, journal or brochure on pipe organs that you are looking for I may have a copy even if the item is not listed in this or previous catalogues. Contact details are on my website
here