PX-13 Mercury Cell (1.35v)
Used for the automatic exposure control of the Bolex 150, 155, 7.5 and 160 cameras (two each); Used for the exposure control in the Vario-Switar 36EE, 86EE and 86-OE lens (one).

Solution: use a Silver Oxide Silver 76 1.5v (SR44) in a voltage reducing MR-9 adapter.

Mallory RM450 (1.35v)
Used for the exposure meter of the Zoom Reflex P1, P2 and P3

This battery was 11.6 mm in diameter and 14.5 mm in height. Here are two solutions, but both require washers or other metal conductor to make up for the height difference.

Solution: Use a zinc air 1.35V Wein Cell MRB675 (11.6 mm diameter, 5.4 mm height)
Solution: Zinc Air Cell ZA675 1.4v (or Z675PX) (11.6 mm diameter, 5.4 mm height)

PX1 (1.35v)
Used to power the zoom motor of the P3 and K2. (requires two)

Solution: You can use a pair of LR50 (PX1A or A1PX) 1.5v alkaline batteries. It powers the zoom, so the difference in voltage is negligible.

There are other options, and other adapters. Hopefully this short list will help you in finding a replacement.