This will easily be earned over time if you're in it for the long haul by doing daily quests and such, but if you want to bang this achievement out quickly I figured out how to do so today. It requires having a couple Astral Diamonds already.
Go to the store tab
Click the astral exchange
Now go to buy zen. Make an unrealistic offer(Something like wanting 5000 zen for 5000 diamonds.)
Place the offer, then go to listings and cancel your offer. Click the Y button to withdraw your diamonds you placed.
Then repeat those last 2 steps. Everytime you withdraw your diamonds from the exchange the game adds them towards your total for the achievement.