The bulb is 2.5 V2 sub C cells would fit. not sure if your lamp will handle, but in theory it should.
This old light was not designed for modern sub c cells (rechargable, 1.2v either nimh or nicd) it was designed for 1.5v carbon zinc cell, that was same in size, but those are no longer made, last time i saw them it was 35-40 years ago in ussr
BF cells were about 5 mm smaller in diameter and 7 mm shorter than C cells.Is that not
2 * C cells?