the oldest one i can find is on oldapps.com, version 6. but is it possible to find version 5 or 4 or even older ones?

Do you perhaps know the years these versions are from? I might have some old backup CD's which contains Antivir installations since that was my main virusscanner that time from about 6-8 years ago...

EDIT: I don't think I can help you... Just found the actual CD I got AntiVir from the first time and on the cover it says 6.25.00.03... So I'm sure I will not find anything older.
The CD I mentioned Is from the magazine Computer Bild (bought it on a vacantion in Germany) and the CD says 15/2004 (I think week 15 of 2004... Or it was brought out every 14 days...)

EDIT 2: Now I'm digging more and more in my memory about Antivir... When I used it for the first time it was also the time Antivir was big news, every magazine wrote about it and if you'll get a CD with the magazine it was on there as well. Don't pin me on it but something says me that 6.x was the first time Antivir got a free edition. If that's true... than there you have the reason why you could not find anything older on the web and need someone with some old pirate CD's.