The Mandolin & Cittern Source
Luthiers
Here is a list of makers of historical mandolins and citterns by country. Neapolitan mandolins and Portuguese guitars are widely available from factories, so I have focused more here on the unusual, harder to source instruments.
Austria
Name: Karl Kirchmeyr
Website: http://www.kirchmeyr.net/
Instruments made: Baroque mandolin
Belgium
Name: Kristof Braekman
Website: http://www.kristofinstrumenten.be/
Instruments made: Baroque mandolin, Neapolitan mandolin
Britain (United Kingdom)
Name: Paul Baker
Website: http://www.diabolus.org/
Instruments made: Gittern, Mandore, Citole, Orpharion
Name: Bruce Brook
Website: http://www.brucebrook.co.uk/
Instruments made: Gittern, Citole, Cittern, Orpharion, Bandora
Name: Jo Dusepo
Website: https://www.dusepo.co.uk/
Instruments made: Gittern, Mandore, Brescian mandolin, Baroque mandolin, Citole, Cittern
Name: Paul Hathaway
Website: http://www.paulhathway.com/
Instruments made: Cittern, Cithrinchen
Name: John Marlow
Website: http://jmarlowstringedinstruments.co.uk/
Instruments made: Orpharion
Name: George Stevens
Website: https://www.gstevensluthier.co.uk
Instruments made: Gittern, Citole, Cittern
Canada
Name: Brian Dean
Website: http://www.labraid.ca/
Instruments made: Baroque mandolin, Neapolitan mandolin
Finland
Name: Lauri Niskanen
Website: https://www.niskanenlutes.com/
Instruments made: Gittern
France
Name: Ugo Casalonga
Website: https://www.casa-liutaiu.com/
Instruments made: Citole, Cittern, Orpharion, Bandora
Name: Wolfgang Frueh
Website: http://www.lepointdaccroche.com/
Instruments made: Baroque mandolin, Neapolitan mandolin
Name: Florian Jougneau
Website: https://florianjougneau.com/
Instruments made: Gittern, Citole
Germany
Name: Magdalena Groth
Website: http://www.guriema.de/
Instruments made: Neapolitan mandolin, Waldzither
Name: Martin Hurttig
Website: http://www.lautenbau-leipzig.de/
Instruments made: Baroque mandolin, Neapolitan mandolin
Name: Heico Kilian
Website: https://instrumentenbau-kilian.de/
Instruments made: Citole, Cittern, Cithrinchen
Name: Matthias Wagner
Website: https://lutes-strings.de/
Instruments made: Brescian mandolin, Genoese mandolin
Name: Caroline Zillmann & Steffen Milbradt
Website: https://www.saitenspiel-zeug.de/
Instruments made: Mandore, Cittern
Greece
Name: Nikos Agrimakis
Website: https://agrimakis.webs.com/
Instruments made: Baroque mandolin
Italy
Name: Anna Radice
Website: http://www.annaradice.it/
Instruments made: Baroque mandolin, Cittern
Name: Lorenzo Lippi
Website: http://lippi.net/
Instruments made: Brescian mandolin, Neapolitan mandolin
Name: Liuteria d'insieme
Website: http://www.liuteriadinsieme.it/
Instruments made: Baroque mandolin, Lombardic mandolin, Neapolitan mandolin
Name: Antonio Giuseppe Severini
Website: https://www.liuteriaseverini.it
Instruments made: Citole
Netherlands
Name: Sebastien Nunez
Website: http://www.earlymusicalinstruments.info/
Instruments made: Baroque mandolin, Cittern
Romania
Name: Lorinczi Gyorgy
Website: http://lorilute.3x.ro/
Instruments made: Baroque mandolin
Slovenia
Name: Vivi Lieto
Website: http://www.floxflorum.com/
Instruments made: Mandore, Baroque mandolin,
Spain
Name: Asier de Benito
Website: https://www.asierdebenito.com/
Instruments made: Gittern, Mandore, Citole
Name: Jaume Bosser
Website: http://www.bosserluthier.net/
Instruments made: Orpharion
Name: Jesus Reolid
Website: http://ret007ei.eresmas.net/reolid/
Instruments made: Gittern, Citole, Cittern
Sweden
Name: Heikki Rousu
Website: http://www.gitarrmakare.se/
Instruments made: Cittern, English guittar
Switzerland
Name: Jorge Sentieiro
Website: http://www.jorgesentieiro.eu/
Instruments made: Baroque mandolin
Name: Dide Marfurt
Website: http://didemarfurt.ch/
Instruments made: Halszither
United States of America (USA)
Name: Ronnie Banks
Website: https://www.rwbanks.com/
Instruments made: Cittern
Name: Daniel Betsill
Website: http://www.betsillworkshop.com/
Instruments made: Cittern
Name: Glenn Braun
Website: https://www.etsy.com/shop/Glennsshipmodelsetc
Instruments made: Gittern, Citole, Cittern
Name: Paul Butler
Website: http://www.crab.rutgers.edu/%7Epbutler/instrum.html/
Instruments made: Citole
Name: Josh Humphrey
Website: http://jbhguitars.com/
Instruments made: Brescian mandolin