I have recently discovered several videos with the famous study in B minor as a duet. I have not found out who made the arrangements for a duet, and I have not found the sheet music for this version.
It is interesting to listen to this arrangement of the study which uses the study as an accompaniment for a beautiful melody.
Flute & Guitar: Fernando SOR – Study in B Minor, Op. 35, N°22
Duet Guitar & Mandolin
Fernando SOR Study in B Minor Op. 35 Nr. 22 Trio for Mandolin and 2 guitars performed
Duet for two guitars
Guitare classique – Kaori Muraji & Kiyoshi Shomura – Moonlight – Etude O.P. 35 – N° 22
A video of the original study
Fernando Sor: B-minor study
I have not found the sheet music for this duet version.
Sheet music by Fernando Sor at IMSLP: http://imslp.org/wiki/Category:Sor,_Fernando
Sheet music by Fernando Sor in the Classical Guitar Forum: http://www.guitareclassiquedelcamp.com/partitions/fernandosor.html