Well, after further Google search, the same cast of characters came up with the answer here.
Does anyone want to get rid of the shims they didn\'t end up using? Might as well buy from the fellows here since they go to waste otherwise. Not too much money, though, so no big diff either way.
This was Mike\'s post from November which I missed (didn\'t have my new camera then):
\"Some folks have had some difficulty in tracking down focus screen shims from Canon. One reason they\'re hard to google is that Canon refers to them as \"washers\". There are eleven different shims, which vary in thickness. They do not come in a set; they must be purchased individually. Luckily, they\'re inexpensive (~$22 USD for all). I spoke directly to a Canon parts department rep yesterday and here are the part numbers (note that these are for the 5D...I neglected to ask if they were applicable to any other body). My guess is that the part number suffix pertains to the thickness of the washer in mils (again, in my state of glee that I found these things, I didn\'t ask that either):
