The best way I have found to grind this out is to use Wooden Fences. They only cost one diamond each so when you sell crops at a stand to make any amount of diamonds you should be able to place one down. You can break these fences down using
and you will get your diamond back. Repeat this for the 1,000.
However you may unlock this just by playing if you care about decoration and places fences around crops and street lights and such.