You can purhase APs (or activate vouchers) at Guest Services at all Theme Parks (located to the right of the turnstyles at MK and EC and to the left at MGM and AK) or at Guest Services at DD.
They may be ordered in advance thru the DVC website or MS, but would still need to be picked up at Guest Services. Make sure you have your blue DVC card and a photo ID wherever you pick them up.
Enjoy!