You can get a cold shoe from a broken 1970's camera, any one will do.
Make sure the burrs are filed off the bottom of the shoe after you dismantle the camera for the part.
Get some 3M (or similar) double sided tape (the thick stuff) and put it on the shoe.
Leave the tape covering on until you find out where you want the new cold shoe with finder on top of the camera.
Place the finder in the shoe and "mock up" where the best location for it would be, making sure the finder is properly aligned.
Once you've found the place where the finder will sit, clean off the top of the M8 with rubbing alcohol to remove any oil.
Firmly stick the double sided tape to the camera and there you have it.
This is a non-permanent, very inexpensive (yet inelegant) way of getting this problem solved.
Phil Forrest