Sour curry paste is one curry paste that most people don't buy, but make it themselves right before making sour curry. The core ingredients in sour curry paste are dried chili peppers, shallots and shrimp paste. Other added ingredients such as garlic, Chinese keys and fresh turmeric depends on the region and personal preference.
I add garlic to mine. The amount of garlic should be minimal compared to shallots. Many people, including my mother, add Chinese keys to tame the fish flavor and add a nice aroma to the curry. Southern Sour Curry Paste is made with fresh turmeric and garlic.