The remains of the Communist Battlefield are located at the end of a small road behind Ban Huai Kon village. There is a reconstruction of what was once a battlefield zone, until about 30 years ago the area was partly off-limit due to mines. It still is a military base and there is a small museum, that is not always open. Just ask one of the soldiers to unlock the door for you. The Remains of Communist Battlefield can be visited all year around, daily and entrance is free. But the museum is not always open. The remains of the battlefield are nearby the village Huai Kon, what is about 140 km north of Nan town. For more information about Nan province have a look at Destination Travel Guide Nan.
Easiest would be to go there with your own transport, as there is no public transport going there. Just follow route 101 to Tha Wang Pha, Pua, Chiang Klang, Thung Chang and then into the mountains to Huai Kon. At the intersection in "town" is a small road behind the local hospital. Follow that road and at the end is a army base where is also the former battlefield zone. You could also take the mini-van from the bus-station in Nan town to the border and just before the border get off. Then find local transport to the former battlefield zone.