Well, first off I do have the knights of the nine expansion and the Shivering Isles

I want to get something that looks like that, or Duncan's sword, I know a Katana is a good choice but its not thick enough
So if anyone knows of an item like that I'd appreciate it.

Not to sure what that sword looks like, but can't think of anything that would look like a katana but thicker. If you are on pc there is probably a mod that you can find to add something more to your tastes

Elven short sword http://www.uesp.net/wiki/File:OB-items-Shortswords.jpg or dagger http://www.uesp.net/wiki/File:OB-items-Daggers.jpg are the closest un modded I think, pretty close imo.
There are some blades whitewood - or something wood in mods ( the one I know of is OOO ), but it depends on if you can mod and search the sites.

For certain blades I think daggers in DA, the blade chillrend matches http://www.uesp.net/wiki/File:OB-item-Chillrend.jpg