You can get them at any Guest Services window at the parks - just have your member ID and photo ID.
If you want to pre-order vouchers : Login to the members website (dvcmembers.com), click on Member Priviledges > Member Perks > Walt Disney World Resort > WDW Annual Pass Savings ... > Follow the link in the middle of the page under "How to Purchase a Pass". They will then mail you vouchers that can be redeemed at Guest Services anytime in the future. This is a good way to lock in today's prices for a future trip.