Yeah, but what is the price of that? I am considering trying to build the rifle.
I looked around and I don't even seem to have found any decent parts suppliers.
Well, none of them are what I would consider cheap, but there are kit options from $500 and up:
Sitting Fox has a Tennessee Poor Boy squirrel gun kit, although it doesn't have a swamped barrel, you can get it with 3/4" flats that should be quite light. They may be able to add a swamped barrel at additional cost. http://www.sittingfoxmuzzleloaders.c...el%20Rifle.htm
Track of the Wolf has a couple lightweight kits in .40 caliber: http://www.trackofthewolf.com/Catego...T-JP-GAB-FLINT
Dunlap Woodcraft has an Isaac Haines kit available in the smaller calibers: http://www.dunlapwoodcrafts.com/Comp...ainesRifle.php
TVM Iron mounted PA rifle available with swamped barrel: http://www.avsia.com/tvm/pennsylvania_iron.htm