CIMRM Supplement - Statuette of Cautopates. Porto Torres, Sardinia.
This seems to be the only known Mithraic item from Sardinia.
The museum, the Antiquarium Turritano, is close to the archaeological area of the Great Baths, known locally as "Palazzo di Re Barbaro", and holds the finds from the Roman city of Turris Libisonis. The site guidebook is online here (PDF) and contains a picture of the monument on p.41 as fig. 24: "Rilievo mitriaco con raffigurazione Cautopates, frammentario (metà III sec. d.C.). Porto Torres, Antiquarium Turritano." From p.43:
And on p.106, in a detailed description of the museum and its show-cases, for the upper floor: