Where can I find anti-virus software for Ubuntu on the Mini 9 ?

There are no anti-virus programs for the Ubuntu Desktop itself as they are typically not needed.

Anti-virus programs in Linux are mostly used on server to filter emails where viruses transit, to prevent their propagation.

You can read more about antivirus software and Linux here:
http://www.linux.com/feature/60208

One important quote:
"So Linux is bulletproof? No. Bulletproof is one of the last stages of drunkenness, not a state of security. Linux users, like users on every operating system, must always be aware of security issues. They must act intelligently to keep their systems safe and secure. They should not run programs with root privileges when they are not required, and they should apply security patches regularly. "

"Root privileges" here refers to any software that runs with administrative rights. You will notice such programs as for your password.

I am oversimplifying a bit here, but I trust this is enough to answer your question.

Fabián Rodríguez suggests this article as an answer to your question:
FAQ #308: “Mini9: Where can I find anti-virus software for Ubuntu ?”.

      I use f-prot. It's free to Linux users and has free updates. Look it over at http://www-fprot.com/ and see if it works for you.

ClamAV with the (clamtk front-end) is in the dell-mini repository and it works quite well. The version in the repos is a bit old, newer are available in this PPA:

https://launchpad.net/~hardybleed/+archive/ppa