Please put in a link to this arrangement on Sibley's web site.
La séparation. Nocturne von M. J. Glinka. [Bearbeitung] für Violine, Viola alta oder Violoncell u. Piano von Hermann Ritter.
The original for piano, and Ritter's arrangement for cello and piano are already on IMSLP.
The viola and piano arragement by Ritter should be available somewhere. Unfortunately it is not on Tarakanov's Russian site.
Thankyou for your treasure store of scores.