For what it's worth, you don't need to mount fontsrv anywhere.
You can just use 'fontsrv -p .' to list the fonts,
and then refer to them as /mnt/font/Name/SIZEa/font.
For example:

/usr/local/plan9/bin/acme \
    -f /mnt/font/LucidaGrande/12a/font \
    -F /mnt/font/SourceCodePro-Regular/12a/font

In that form, acme will "open" /mnt/font/... by reading fontsrv -p's output.

Best,
Russ