Atelier Bousoirr in France now offer Octave Viola strings… follow the link below or visit https://www.atelier-boussoir.fr/

Link to Octave Viola String Page
https://www.atelier-boussoir.fr/boutique/cordes/jeux-de-cordes-speciales/

I have not tried these strings, yet, nor do I have any affiliation to Atelier Bousoirr, but one of my customers has and both he and his luthier were impressed.