I've gotten an old Leica IIIf kit including a flash attachment (Ceyoo), all in fine shape. But the battery is dead (no surprise, it's gotta be decades old by now). The battery is a 22.5 volt "hearing aid" battery about the shape and size of a modern 9 volt battery. While I would not expect that there are some old Leica equipment experts reading here, perhaps someone knows where I should go to find out what might be available today.
Thanks for reading.