Here's the deal...
Some seedbanks will sell you seeds as a "novelty" or "souvenir" item (lol as if you never planned on putting the seed in soil).
If the packaging is discreet enough, it won't catch the attention of US Customs, and you'll have your seeds.
If the packaging says, "CONGRATS ON THE PURCHASE OF YOUR MARIJUANA SEEDS!!!" all over it, chances are you'll get a letter from the government stating that your mail was confiscated because it contains illegal contraband.