So, I decided to make my own concentrate. You'll likely need to hit up a Fruiticana first (as not too many people keep green cardamon pods stocked in their cupboard). I've been experimenting with a few batches, and change it almost every time. Below is a guide, but be sure to play with it a few times until you find the ratios you like. It should keep in the fridge for a week or so, though it likely won't last that long. Enjoy!