The only GEC purchase channel is via official store transactions in the game. Any websites or services outside claiming to offer GEC purchase will not be able to provide you GEC and are likely to steal your account and password. For your own safety we encourage you not to try any of these channels, as your account details will be in danger and you will gain nothing.
Please also note that attempting to use any third party purchase channels is in violation of our player policy and is likely to result in a ban on your account.