Here is a link to some of the Marine Protection Act:

http://www.fws.gov/laws/laws_digest//marmam.html

Not sure about getting a sporran through customs, but I think if it is of a certain age it will be fine. You might want to look into that, you could also look into the alternatives that are used in the US for example USA Kilts has one here:
http://www.usakilts.com/sporrans.php

There was a thread not long ago with some good pictures of one being used at a wedding:

http://www.xmarksthescot.com/forum/s...ad.php?t=28035