Where can I download windows vista legally?

Hi all, I have a dell computer which originally had vista business oem on it, and it has the license sticker still on the thing. I’ve long since installed another OS on it, and don’t have any disks that came with it.

I am now selling the computer and want to return windows vista back on it with the license, but I can’t find anywhere to download the original, non-hacked iso for it. Bitorrent is full of hacked, cracked, creepy, who-knows-what ISOs, but I just want the original legal version of it so I can use it with my key. sigh