Free public domain sheet music from IMSLP / Petrucci Music Library
Leipzig: C.F. Peters, n.d.. Plate 3941.
Public Domain [tag/del]
The score is marked 'III' not because there are only parts for the third duet (there's only one here), but because it is the third work in a compilation of Spohr violin duets. (The others in the collection are submitted to separate pages.)
||Duo for 2 Violins, Op.153