Be conservative when using cardamom because it can be quite overpowering when over-used.
Purchase cardamom seed or ground cardamom in most grocery stores. Whole pods, green or brown can be found in India or Asian grocery stores.
Ground cardamom is the most perishable so it is best to purchase in small amounts and discard after 3 months. The seed will last longer and can be ground. The whole pods can be stored at least for a year.