I am going to provide links here to businesses I have had good dealings with and good sources of information…
business directory
VanHalteren’s Music Centre in Lindsay, ON, Canada: http://www.vhmc.ca/index
The Interesting Music Shoppe in Wilfrid, ON, Canada: http://www.interestingmusic.ca/
Currie’s Music and Antiques in Gravenhurst, ON, Canada: http://www.facebook.com/curriesmusic
Hank 2 Hendrix luthier (guitar repair) services in Peterborough, ON, Canada: http://www.hank2hendrix.com/
The Guitar Corner in Kitchener, ON, Canada: http://www.theguitarcorner.ca/
The Fishin’ Musician in Waterford, ON, Canada: https://fishinmusicianstore.com/
coolguitars.ca in Kingston, ON, Canada: http://www.coolguitars.ca
StringKraft custom decals Georgia, USA: https://www.etsy.com/ca/shop/StringKraft
eezyreeder, Pennsylavania, USA: http://www.eezyreeder.com/
information
The Harmony Guitars Database: http://harmony.demont.net/
NOTE: The Harmony Guitars Database is currently down and being moved to a new server, it can be accessed via the internet archive here: https://web.archive.org/web/20200806133357/http://harmony.demont.net/
Made In Chicago Museum’s history of Harmony musical instruments: https://www.madeinchicagomuseum.com/single-post/harmony-company
chasingguitars.com History of Harmony (also Histories of several other manufacturers): http://chasingguitars.com/harmony-history/
Silvertone World: http://www.silvertoneworld.net/default.html
Kay Vintage Reissue’s library of catalogues and a complete listing of every Kay model and the years they were produced: http://www.kayvintagereissue.com/#catalog
Oscar Scmidt Company: https://www.leavingthisworld.com/oscar-schmidt-company-1897-c-1939/
Stella Facts: http://www.stellaguitars.com/about/stella-guitar-myths-factoids/
The Slingerland Stringed Instrument Pages: https://www.slingerlandguitar.com/
“Kent” electric guitars (most made by Teisco/Guyatone/Kawai): http://www.kentfoto.com/music/KentGuitars/varieties/index.htm
Vintage Guitar Catalogs site: http://vintage.catalogs.free.fr/Index.htm
Egmond, vintage Dutch guitar maker: http://www.egmond.se/egmond_se_History.html
Here is another Egmond link, audio is in Dutch. I am in contact with the owner of the video and he is looking into an English translation: https://siertvandenberg.nl/
Charles Brasher (Toronto area pre-war resonator builder): http://www.notecannons.com/charles_brasher/
The Amateur Luthier’s listing of Kay/Harmony/Regal built 3rd party brands: https://www.stlamateurluthier.com/2019/06/vintage-chicago-built-guitars-brand.html
Jedistar, an Australian collector’s free information site for guitar enthusiasts: http://jedistar.com/category/guide/
A fairly comprehensive list of Japanese manufacturers and the brands they made: https://spinditty.com/instruments-gear/Japanese-Manufacturers-of-Made-In-Japan-Badged-Guitars-from-1950-to-1980
An excellent article on Reverb about Japanese manufacturers: https://reverb.com/ca/news/its-not-all-teiscos-look-at-60s-japenese-guitar-makers
My Rare Guitars’ account of the history of Kawai: https://www.myrareguitars.com/the-story-of-kawai-guitars
The World of Musical Instruments Brochures, (Japanese manufacturers, catalogues too): https://brochures.yokochou.com/en_index.html#
audio/video samples
Roadtoast Guitars: https://www.youtube.com/channel/UCSMZqZHbnch-sgx6zAcCn0g
Gibbons’ Guitar Emporium: https://www.youtube.com/user/GibbonsGuitars/videos
Dan Lambert: https://www.youtube.com/channel/UCo-O5oAwmooAR3iXael7Cgg/videos
drowninginguitars: https://www.youtube.com/channel/UCzLRpB_ThIJ39wmgfBozASQ