One other option would be to keep the M2 and get a Voitlander VC II meter. This is a meter which slides into the accessory shoe of your camera, making a neat little package. Has the same field of view as a 90mm lens, so makes it easy to meter, looking through the the viewfinder and using the 90mm framelines (or nearest equivalent) to find a suitable subject to meter off of. Meter uses two 1.5V button batteries.
This meter can be purchased through Cameraquest in the U.S. They have a website you can order off of.
Only problem might be if you have to use an auxiliary viewfinder as well as the meter. In that case you might try to find the double accessory shoe Voitlander used to make. They made several models, designed to fit certain brands of camera (i.e, one model to fit Leica screwmounts & Leica Ms, another model to fit Nikon rangefinders..)
These double shoes have been discontinued by Voitlander, but you might find one if you look hard enough. Be sure to get the model designed to fit Leica Ms...