(fonts/amsfonts/sources/modes.mf) was dated
The canonical location would be fonts/modes/modes.mf.
I see that's at version 3.3, though, not 3.4. Sigh. I'll try to
straighten that out.
amsfonts is nothing I have control over or input into.
The actual original location for modes.mf is ftp://tug.org/tex/modes.mf.