Unfortunately, I do not know where to forage fiddleheads, though I have a friend who let me do some picking on her property a couple years ago. Fiddleheads rank right up there with asparagus in terms of being delightful to eat. If I had to choose between the 2, I'd choose fiddleheads. Therefore... they just might be my favorite vegetable. They can be bought here when in season. There is an Indian reservation about 25 mi. away. Those folks harvest and sell a lot at good price in the College town that their reservation island abuts. Also, many Mainers collect and sell fiddleheads at road side when they are in season. Absolutely yummy, buttery flavor, with melt in the mouth texture. They MUST be well cooked, otherwise, they are toxic.
People guard their picking places, thus... I can't get anyone to take me out harvesting! Similar to hunters who won't tell anyone where their favorite hunting spot is... or Mushroomers who guard their morrel sites! Or, fishermen never telling WHERE they caught the big one.