VirusTotal is a good start if you're willing to fork out $$. After that you can find companies who will sell you feeds. After you've up and running on people'

VirusTotal is a good start if you're willing to fork out $$. After that you can find companies who will sell you feeds. After you've up and running on people's computers there are sample sharing agreements between AV companies, but you need to have something of your own to share before they're going to give you theirs.