I've never found any nation of origin on any of the packages of sphagnum I've boughten the one exception was the old Mosser Lee brand of sphagnum from Wisconsin (also farmed in Wisconsin). But that stuff was crummy, rarely did sphagnum moss grow from it, but lots of other weeds and stuff did. I don't belive ML is stilll in business, at least, I haven't seen it for sale in many years now so you should be safe with any of the current brands out there.
I think the key to getting it growing (no matter the origin) is to shred it so the spores are released from the "heads" of the sphagnum ropes, anytime I've just wet it and threw it in a tray or terrarium as a substrate, it just grew algae, forest "cap" moss and ferns. Grind two handfuls of compressed dried sphagnum together (wear a dust mask or use your tee shirt pulled up over your nose and mouth as a mask while you grind), you'll make a finer sphagnum powder that way than wetting it and then trying to chop it with sciscors - doing it that way also makes it easy to cut yourself - which I've done!