If you are willing to mill your own lumber any wholesaler who supplies the cabinet industry in your area should sell #2 or #3 common sugar pine in 1" X 12" in lengths up to 16' long. In Tidewater Virginia there are at least 4 vendors who will sell to the general public on a cash and carry basis. When I ran a cabinet shop, we bought #2 sugar pine 2400 bf at a time and used about that much in 3 weeks.
You might also ask around the local cabinet shops and see if they will sell you some shorts that otherwise would be scrap. I sold Red Alder scraps by the grocery sack full to fishermen who wanted them to smoke fish and used the off falls from basswood in my own model making and poplar strips to make spline roadbed. Fall and winter are also a good time to get kindling from local shops also.
BTW, I use a Byrnes table saw to make all of my modeling lumber. http://www.byrnesmodelmachines.com/index.html?id_mm=1220MM920589
I am currently looking for a small quantity of old growth Red Spruce from West Virginia to complete a pair of models of buildings from what is now the Cass State Park. Any help out there?