I really love the idea of this weapon, but the ones you find seem really underwhelming compared to other weapons.

I installed the Rogue Rebalancing Mod as well and they add some really cool options for thieves, but sadly no katanas.

Any recommendations?

i made two; one that turns orc to ice on crit and one that caused panic in vamps... they both proved more trouble than they where worth
one point, the game / build will tell us which mods you can use i.e, what works in Bg1 will not work in Bg1EE