Lynda Sayce's theorbo website: www.theorbo.com
Facebook group: www.facebook.com/Tiorba
Francesca Torelli has published a tutor for theorbo: www.utorpheus.com/index.php?route=product/product&product_id=1550 published by Ut Orpheus Edizioni
Tiziano Bagnati has edited Cadenze e Passaggi diversi for Theorbo from the Modena manuscript G 239, one of the principle instructional sources, published by Ut Orpheus www.utorpheus.com/index.php?route=product/product&product_id=475 and also a collection of newly composed etudes.
A list of historical sources, with downloadable facsimiles where available, can be found at:
www.lutelibrary.com/print-sources/instrument/theorbo
Diego Cantalupi, thesis on theorbo as continuo instrument drive.google.com/file/d/1jixx2nLDXZ8MYhomBmHWPeaXiUMfYBiA/view
The term 'theorboed' was loosely used for all sorts of extended neck instruments, for instance:
‘German theorbo’ essay on the Accords nouveaux website:
www.accordsnouveaux.ch/de/Instrumente/DtTheorbe/DtTheorbe.html
Theorboed cittern, essay on the Accords nouveaux website
www.accordsnouveaux.ch/de/Instrumente/Theorbenzister/Theorbenzister.html
See also Swedish theorbo