It is a commercial product. A friend who travels more widely than I, gave me a bit to taste.
Don't suppose there's any chance he'd be willing to reveal his methodology? I could bake him cookies :-P
Hopefully, with the impending release of Haus Alpenz Batavia Arrack, (July 15 according to their website,) some recipes for Swedish Punsch will surface!
Mostly, from this version, I get the flavor of Arrack and a hint of cardamom.
I have another friend who is traveling to Sweden this summer, and I've given him the assignment of bringing me back a bottle of Carlshamm's Flaggpunsch.