Tor missing

Looking at the Ubuntu package list, it doesn't look like there's a tor package there either. Which means it's probably isn't a case of it having been removed accidentally. Still, I don't know why there isn't a tor package.

Look here for the tor package history in Ubuntu repositories.
As far a I know Trisquel repositories are cleaned, from proprietary software, versions of Ubuntu's repositories; well, plus minus some things.
The current version, Awen, is based on Karmic.
Also, here you can find instructions on how to install and use tor on Ubuntu(based-os).

A bit off topic but be sure to also read the Tor Wikipedia article's weaknesses section.