A quick search indicates the Hi-Matic E takes 2 x 1.35v batteries. In other cameras of that vintage with that voltage requirement I've had good success using regular zinc-air "hearing aid" batteries, normally available at pharmacies and department stores. I believe my cameras take the "625" size equivalent, but I don't have it in front of me right now. You can also get photo-specific zinc-air batteries such as the "WeinCell", which is supposed to last longer than the hearing aid version, but the last one I bought was DOA, so hearing aid batteries it is

If they don't fit properly you can pad them with tin foil or springs or something else conductive.