There are plenty of places on the Web to do this. Windows 3.1 is abondoned by M$ and plenty of people have it. Heck i have all versions of Windows from 1.0-Vista.
Hit me up on PM or MSN and i can give you some details.
It's abandoneware and therefore technically legal to download. I'm sure the good ol' mods are going to lock this thread anyways but there are a number of reliable ways to get old OS like this.
No body knows for sure if it's legal or not, but it won't be lock if unless somone post a link to a warez site or something. Just don't do that and conduct your business else where.
the legality of abandonware has been argued for a long time. But as i said previously very few companies make a fuss over sharing it. It would cost them more $$ than it is worth.