They were available in Aion (NA) until 2/26, 2012, then discontinued. They are still available in Aion (Europe).
To claim a Veteran Reward in Aion (Europe):
Your rewards are mailed to you, via the in-game mail system, and usually arrive in seconds. They are sent by Shugo Express, so you can click on the package icon by your minimap and a Shugo courier will appear to deliver your packages! (You can also pick them up at any mailbox, of course.)
In Aion (NA), the time period is a calendar month, regardless of how many days are in the month, so if you started playing on launch day, 9/22/09, your rewards will be available on the 22nd of each month, thereafter. Each paid subscription month (they don't have to be continuous) will advance your level of rewards available.
In Aion (Europe), the time period is equal the amount of Gold Pack (30 Days) (PW/AA) that have been activated for the given account. The progression is updated as soon as the items being activated. As example, opening 2 Gold Packs in a row, will advance progression of two months. On the accounts that were transferred from NC service to Gameforge service, the time period is added to the previous time the account have earned in NC service. As example, an account who were previously accredited 5 months of VR when in NC service, if opens 2 Gold Packs in a row, will advance progression of 2 months, giving access up to VR's 7th month.