Dusepo, Have never seen anything smaller than a 000 size guitar kit and I've been shopping kits off and on for the last two+ years.
No one makes a baritone kit that I'm aware of.
The nearest to what your looking for would be a tenor kit. Top of the line from Pete Howlett or one of the StewMac kits. For the experience of building a kit, those would be my recommendations.
The width at the nut is very near that of the baritone with the scale length about three inches shorter. The point here is that there is enough room for six strings. Conversions have been done and threads to that end have been posted on this forum.
Fred