If the revolver is that old, and made by Euroarms, and called a "New Model Navy", it may have the smaller Remington Navy sized frame. In that case, the modern made Kirst or R&D (Howell) cylinders will be too large, as the Pietta and Uberti 36 Navies are made on the 44 frame.
If you have a 44, compare them, if the cylinders interchange, you can search for a 36 cylinder. Ask VTI gunparts about cylinder for the older Euroarms.