Gift & craft shops usually have them. In Wolfeboro, these come to mind but, in view of the covid situation, I'd call first instead of doing in-person scouting — the staff in all of these shops know their stock. Some of them carry cards by journalist Elisse Paquette, who does lovely nature photography and who may have some Christmas-y ones.
https://blacksgiftsnh.com/
https://www.gabriolabakery.com/gifts
https://butternutsgooddishes.com/
https://www.thecountrybookseller.com/