Tamarind paste is hard for me to get in my area, but it's a key component to this meal. There are a few substitutions you can use, but I'd highly recommend ordering some online if you can. I tried vinegar and brown sugar as a substitute, and… meh. If you're going to improvise, lime or lemon juice with brown sugar apparently gets you closer to that fruity tang tamarind has next time I'll try that instead.