Ways that I can see:
1. Wait for a version to be compiled for Saucy
2. Edit sources.list to include an earlier version (e.g. add deb http://apt.tvheadend.org/stable Raring main)
3. Compile a version yourself and install using dpkg
4. See if you can download the .deb file from the repository and install it locally
I'd have no concerns about (3), so I don't see why (2) or (4) wouldn't work as well - although I don't know how you'd do (4), I must admit. There may be some dependencies you'll need to sort out for yourself as well since apt-get can't handle those for you.
EDIT
The files in http://apt.tvheadend.org/stable/dists/raring/main/binary-i386/ describe what you'd download, from where and with what dependencies (I chose Raring as the closest for you).
The binaries are then in http://apt.tvheadend.org/stable/pool/main/t/tvheadend/
I suggest you take a backup beforehand, or do some more research, as simply installing could result in some undefined results.