Kaiser caps are made in just about every size you would need. I even got a tiny one for the back of my 30mm Rokkor. B&H carries them.
Measure the outside diameter of the lens and get the cap with that measurement.
The only thing Kaiser does not make is half-millimeter (0.5mm) sizes. The Eskofot Ultragon needs a 0.5 mm size.
Guess it's time to replace the battery in my calipers then!