Your best course of action is to either identify a dealer near your point of entry into the US and make your purchase or have your stateside host do it for you.
When you pass they send back a code to activate your taser.
You're making an assumption that this is required everywhere. Internet sources don't perform this with any consistency.
Do I have to register my C2?
Yes. Your TASER C2 is inactive at the time of purchase. You need to register it with TASER International, either online or by phone, and pass a felony background check before receiving the activation code. Some states and cities might have additional requirements so check your local laws carefully.
any autherized dealer for taser will have you do a background check
any autherized dealer for taser will have you do a background check
C2 is actually better for civilian use as it conceals better than the x26 and doesn't look like a gun or anything threatening.