The one I find most practical, though it requires an initial outlay, is a CRIS-type adapter which resizes and lowers the voltage of commonly available silver cells.
You *can* make such an adapter yourself, though it isn't that simple.
Alternatively, you can have the camera's meter re-adjusted for 1.5 volts and use a silver cell + a wad of aluminium foil to adapt ther size. Or even just adjust the ISO setting yourself to compensate.
Hearing aid batteries essentially work like Wein cells, but are muich cheaper (also need some size adapting trick like a foil wad).