This is a list of crank organ builders' websites that particularly impressed me and that I found while browsing the web. It is by no means exhaustive and I will be glad to add to it on request.
I have divided it into two sections: Italian and foreign builders.
Italian builders
As far as I know there are no companies building crank organs in Italy, except for a skilled craftsman of Belgian origin, Christian Casse, who presents his projects both on his own site http://www.miositoweb.info/christian.casse and on the AMMI association site.
Another useful address for enthusiasts is GIRALANOTA www.giralanota.it, which illustrates the activities of the Giannotto family, well known for restoring barrel organs and pianos and for arranging music on rolls and cartons. A large repertoire of arrangements is available. For beginners I recommend the page about the Clin Clan.
Foreign builders
www.jaegerbrommer.de
A German company producing splendid organs, particularly interesting are those with a rhythmic accompaniment section.
www.raffin.de
Another German company with a very wide range of truly professional organs.
www.ragtimewest.com
A US company which, besides a myriad of mechanical music machines, also offers an organ sold as a kit.
www.leludion.com
French company with a wide range of beautiful organs.
www.deanorgans.co.uk
English builder.
www.stinsonorganco.com
English builder offering many MIDI solutions.
www.limonaires-fournier.fr
Marc Fournier presents a wide range of instruments, from small portables to band organs and trailer-mounted ones.
www.alanpell.com
A famous English builder who, besides complete organs of various sizes, offers many semi-finished parts for building your own organ. He also offers an original MIDI system for the instrument.
www.hofbauer-orgelbau.de
German builder with a range of instruments.
www.drehorgel.net
Orgelbau Stuber Berlin.
www.orgues-de-barbarie.com
Site of the French builder Odin, offering a range of very beautiful instruments.
www.castlewoodorgans.com
Castlewood Pipe Organs is an Australian company producing a busker organ kit with laser-cut wood for the DIY enthusiast. The instrument uses the same musical scale as John Smith's organ. Construction is made easier by parts with interlocking corners like a castle, hence the name "Castlewood", giving strong, light joints at a very affordable price. Music rolls for this instrument are available from both Melvyn Wright and Ed Gaida.