Eaeabee1,
Finding Fowler kits is tough if you want anything other Than 20ga. I make 2 to 3 a year and I have started ordering my barrels a year in advance. (I try to have a 2 year inventory). I then have the barrels sent to Dave Keck of Knob Mountain Muzzleloading along with my stock blanks. I have him inlet the barrels and drill the RR hole. If he has a profile I like I will have him profile the butt stock and lock panels also. The fix to your long LOP is to have Dave leave the butt stock square and you can get at least another inch of length. I get most of my furniture from Dave or Tip Curtis. I'm pretty sure you won't find a kit with 15" LOP! Good luck, Bob