Smo already covered it pretty well. But, besides Kibler, there are Jim Chambers, Track of the Wolf, Tennessee Valley Arms, Dixie Gun Works, and some others. These are generally "high end" and are not cheap however.
If you really want to try your hand at putting together a kit, unless you are an experienced woodworker, I would recommend one of the relatively "cheaper" kits from Traditions, or Lyman to start off and get some experience at putting these things together. Most of the work is already done for you with these kits. You might have to shave off a little wood here and there, then just screw it all together and put a finish on it.