I would ask at Nordic Preserves Fish & Wildlife (in the Essex Market) - I doubt they'd have it in stock but they might be able to get it for you.
If they can't get it for you, I imagine no one can - the only other option is to have it shipped over from Scandinavia or an EU country that sells it.
Butik Hemlängtan will ship it to the US, it's only about $10 a can... but the shipping would be around $35, give or take. Not sure if you'd want to spend that much:
Or, of course, you could make it yourself if you've got a nice sterile room and about six months to stink it up. It's almost new herring season, perfect time to start a batch.