Bill,

Check with John Appleton for a nice clean GP action. John has a bunch of GP's from England. They are not the cheap rode hard put away wet well worn surplus guard guns. If interested I would be willing to run out to John's for you and find you a nice tight clean one for John to ship to you.

Contact John Appleton - http://users.erols.com/apple1co

Check with Chick Donnelly for a barrel. He doesn't make bore barrels, but my money says he knows where to find one.

Chris Dieter at Pac-nor doesn't list any but my guess is he would build one.

Krieger has a 4 bore listed at http://www.kriegerbarrels.com/