Hi Rich
Here it is...
# Debian GNU/kFreeBSD "Jessie" 8.x amd64
Last try today, I upgraded all packages and worked like a charm.
It happened in past, and could happen again, that
httpredir.debian.org points out to a mirror which has decided not to host a copy of "jessie-kfreebsd".
This is a bad behavior of the mirror, but we cannot impose it to do.
The simplest solution, is to try again to apt-get install, as the next try point out to another mirror and the majority of the mirrors now have jessie-kfreebsd.
Enjoy the upgrade! ;)
gl