I am afraid that you are going to have to stick to google, as those sorts of sites don't stay up for long Any that I knew have long gone.

You might also search for "keyloggers" and "trojans" for a bit of variety, also to show you what AVs frequently miss.

Try looking for "virus toolkit" and "worm toolkit" then you can make some of your own?

Your school might be able to get some samples if they make an official request to their AV supplier?

Try and find people with reasonable French, german and Spanish as I have found more sites in those languages, the times that I have looked.

Another one is "warez" as those sites sometimes have a virus section.

I would suggest detaching one of your 10 machines and connecting it independently to the net for the collection process. Do NOT do it on your own computer, the sites where you can find that sort of stuff are NOT safe!

Cheers