Link from the revenue smart contract will be sold on exchanges once they support it. Until then, Link can be purchased directly. Any Link purchased at this time will not be delivered until the livenet has been activated and sufficient funds have been released from the revenue smart contract.
Alternatively, Link can be mined directly.
If you wish to purchase Link please email email@example.com. It is currently available at a price of 0.01 USD per LINK. Payment can be made via any cryptocurrency.