I doubt that most Americans who saw your sporran would have any idea as to what sort of fur was on it, as sealskin is illegal to import into the U.S., so customs might have a problem with it. Other furs such as mink, otter, badger, wildcat, etc. are all perfectly legal here. Rather than risking having your sporran confiscated, you might do well to either rent or purchase one for wear in the U.S. We have a number of firms here that rent Highland attire, and it shouldn't be too much of a problem to do that, though you might pick up a rather cheap one off of ebay that is made with rabbit fur, which will get you by, even though it may not be as nice as the one you normally wear.