There are multiple sources for radio manuals / radio instruction books, electronic test equipment manuals / electronic test equipment instruction books and radio schematics / test equipment schematics. Sometimes the offerings are originals but more often they are paper copies or PDF scans. Some sites have free downloads but on most sites the offerings are for sale. Over the years I have noted these sources when I ran across them. This is the resulting listing:
Free or Links:
http://www.ebaman.com ELECTRONICS Test Equipment
http://bama.edebris.com/manuals
http://www.ac6v.com/manuals.htm
http://www.repairfaq.org/REPAIR Manuals
http://www.dxzone.com/catalog Manuals
https://archive.org/details/texts
https://groups.io/g/ManualExchange
For Sale:
http://www.imradioha.org Antique Radio Literature
http://www.smcelectronics.com/sams
http://www.logwell.comtech oscilloscope manuals
http://www.vintagemanuals.com/
http://www.oldradioparts.com/pg3
http://www.hamradiomanuals.com/
http://www.surplussales.com Manuals
http://www.qservice.tv pdf_catalog
http://www.recycledgoods.com manuals
http://www.ebay.com.au
manuals
http://www.w7fg.com/index.html
http://stores.ebay.com/Carols Manuals and More
http://www.vendio.com/stores - military radios catalog
http://www.smcelectronics.com sams
Another listing like this one, but antique radios only:
https://antiqueradios.com resources Schematics/
Note that this is just a listing not personal recommendations. I have not had dealings with any of these sources, and I accept no responsibility for deals gone bad - you are on your own. However, I would like to hear from you if a source disappoints you, if there are dead links or if you know of additional sources.
Main Site - The Inland Marine Radio History Archive
Links checked/updated - 11/09/2020 Page code revised - 02/23/2021