Does anyone have a copy of Mazur's unpublished notes:
Arithmetic in the geometry of symmetric spaces
that they are willing to post? Thank you!
I sent the link to your question to Barry Mazur, and he has very kindly sent the paper to me. I've got it scanned and sent it back to him, so if you ask him gently, he'll send the pdf file to you.
I'm happy to have helped you in a small way, because there is a very kind soul who helps me in a big way. His name is Dino Lorenzini, and he has sent me some papers which cannot be found anywhere in the closed disk of radius 3000 km centered at Allahabad. Merci, Dino.
Addendum. With the permission of Barry Mazur, here is the typescript. He'll also put it up on his website.