I'm having a bit of trouble finding Corundum ore. Does anyone know where to find some?

Pretty sure you can get some in Whiterun from the Companions blacksmith and also the armor/weapon shop near the main Whiterun gate. Those are the only places I've specifically noticed as I do all of my smithing there so far.

There probably isn't alot at each vendor so might be best to try similar places in other towns.

I think there's some in Blackwater (or the ruins on the way to Blackwater).

there is a deposite just outsid Whiterun to the right as you leave the gate. its up on top of that small cliff.

hope this helps

Look at this list http://www.uesp.net/wiki/Skyrim:Mining

Thats the most common ore, I find it everywhere and have way too much of it now lol

One of the spots I remember is one of the little islands in the lake west of riverwood.