Another New Englander....this is good we are slowly starting to take a foot hold on this side of the continent. As for your question, I think you are in for a tough time. I would seriously doubt that the wood from a barn built in 1910 had pumpkin pine wood in it.
I am no expert by any means, but I do enjoy logging history and have been living in Maine...in a logging/farming family that has been here since the pilgrims landed at Plymouth Rock, so I think I know a little something about logging and Pumpkin Pine.
I know by 1870 much of Maine and New England had been logged over pretty hard. It was the apex of the logging era. Now it depends on where the barn in question was built. If it was in some far flung town in the center of New Hampshire's White Mountains, where few rivers resided and it would be hard to get the logs to market, then maybe it was built via Pumpkin Pine wood since it would be hard to log those areas over. More then likely it was built from 2nd generation Eastern White Pine. (We are currently harvesting our 3rd and 4th generation Pine nowadays).
You can easily tell. I worked with my uncle once on a 200 year old house in Brooks,Maine and we found some Pumpkin Pine Boards. The grain was so tight you could barely count the growth rings...or at least I had to squint to see them. The color was also quite yellowish, but that might have occurred from being a wall board for so many years. Anyway you know all this since you have some Pumpkin Pine at your house now.
If the 1910 barn wood does not pan out, you have a few options. One is to find a building contractor that specializes in demolishing old buildings. They know what Pumpkin Pine is and most certainly save it out for people such as yourselves. I know of one such person on Route 17 in Rockport, but don't know his company name.
Another option, and perhaps more costly, is to find a salvage diver. They are few in number, but I have heard of some that are dredging log driving rivers and lakes such as Moosehead Lake, the Penobscot River, and the Kennebec Rivers. You will have to do an internet search to find them though.
If you do find some wood, or find some barns our buildings you suspect are made out of Pumpkin Pine, measure the board widths. The widest board you will find is 23½ inches wide. That is because prior to 1776, any tree wider then 24 inches was automatically granted to the King of England for use in the British Naval Fleet. That is a quick way to determine the age of the wood, then go for grain and figure. You may find boards wider then that, but it will be very rare. Boards wider then 23½ were toppled by the wind and that was where we get the term "windfall" to this day.
I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"