Someone asked me for this, and since my source disappeared, I thought I'd post it here.
This is the version of Paint Tool SAI that I use. Obviously, since I already use it, I can verify that it's safe and virus free, and should work on all versions of Windows (I've used it on 7, 8, and 10).
https://www.dropbox.com/s/ilrhvchu5mzfu2q/Paint%20Tool%20SAI%20Anglicised%20with%20Custom%20Brushes%20and%20Transparency%20Mod.zip?dl=0