To answer your question, you can download AVG antivirus 7.5 for linux from here
(see the link near the bottom of the page). Among others it comes in the form of a .deb package for Debian/Ubuntu, so you have simply to download it and issue the command
dpkg -i avg75fld-r51-a1243.i386.deb
A User's Guide is also available (see the Dcoumentation tab in the same page where you download the installation file).
Anyway, I agree with pslacerda: maybe you don't really need an antivirus software for Linux. Looks for documentation about Linux security (or search topics here at LQ) and you will find out how to harden your linux with a good setting of firewall rules and eventually running a rootkit hunter and a filesystem integrity check tool.