I have recently purchased an underhammer from Blue Grouse(Bruce). Bruce is a very knowledgable guy and is more then willing to answer any question, give you help and great advise on underhammers. The parts you get from him is high quality. The metal parts are finished perfectly and are ready for bluing or browning. Plus he includes about 2 lbs of bullets or balls(your choice).
It's my understanding that the underhammer gun kits in white on diplay on his web site for $255 are no longer available. He is having a hard time getting underhammer receivers and I also think barrels. He does have a few receivers, stocks and forstocks on hand. I believe he was getting them from Deer Creek but they are no longer making any underhammer parts and at this time have no plans to make any in the future.
When I ordered my gun I was advised by Bruce that the best thing to do was purchase a barrel from Green Mountain barrel ($125 on sale)and have it shipped to him. He would remove the breech plug, install a new one and drill and tap the barrel for an underhammer nipple. The barrel(stainless Steel) I purchase came with sights, underib, ramrod pipes and ramrod installed. If you send him a barrel blank it'll cost you to have dove tails cut for sights and have ramrod pipes installed.
The stock and forstock I received needed a lot of rasp and file work to get it to look the way I liked(classic underhammer) or if you like a modern looking stock with a plastic butt plate, you can leave the stock the way it comes.
The final cost of the gun including the cost of the GM barrel, barrel work, receive, stock, forestock,and shipping ended up being about $375.
Hope this helps,. :v