Finding good boxes for soap was a big topic at the HMSG Conference.
I mentioned Grigsby Paper Box and the place I'm having mine made (Eagle IMS).
The Box Coop was also mentioned.
But, I just found these boxes on Susan Emery's site. She was at the conference, too.
It's hard to find boxes because regular box making companies don't make boxes that are the shape of soap. You'd think that a basic, smallish rectangle would be easy to find. But, it's not.
Good luck on your box search! :)