I wish to analyze the changes made by a specific virus. For example, Win32.Sality.
Where can I get the sample of this, or other similar, malware for testing?
Contagiodump blog and the spam folder are your best friends
Offensive Computing has about 4,456,929 samples.
Offensive Computing is now offline
http://www.malware.lu/ Has 2,236,674 samples
Here Are Some List of sites where you can get malware for samples
MalwareTIps - Virus exchange Forum
The above url's are An Summary from here
Hope it helps
Github now contains massive repos of malware. The one I linked is but an example.