Guys,
The 12 ga H&R Huntsman (NOT NEF) was made from 1972-1979, the same time as the .45 and .58 calibers were. Unless H&R/NEF (Marlin) have saved some of the old manuals and breech plug wrenches from that era, he won't know any more than he does now. The newer NEF Huntsmans came out about 2002 and the breech plug wrench is totally different than the old style.
goldhound56,
Your 12 ga might have a push in plug with o-ring? The early ones had screw in plugs, the later ones had push in plugs. If yours is a screw in, you may have to make your own tool. Since it has never been fired, the plug should come out easy, whatever the style. If you have a wood dowel you could push out a push-in plug. If the plug has two holes in it, you may be able to unscrew it with two pins welded to a T-Handle. Good luck with Customer Service, I truly hope they had what you needed.
Just a word of caution, if your has a push in plug, be very careful not to open the breach if you have a mis-fire. This condition has been known to turn into a hang-fire as soon as the breach is opened the plug is shot rearward, and has caused serious bodily injury including death. Always attempt to re-fire the charge without opening the breach, if it fails to fire wait keeping the barrel pointed in a safe direction. If and when you decide to open the breach, make sure you are not behind the gun, but off to the side. Just be aware of the danger involved with these types of plugs, it is real. Lots of these guns have been retired due to this condition, and it was the lawsuits because of these breach plugs that took down the old H&R, before NEF and Marlin.
A bit of information.
http://www.thefirearmsforum.com/printthread.php?t=12937