What sour spices are there?
Amchoor (mango powder), anardana (dried pomegranate), and, if you include pastes, tamarinde come to mind.

They all have a tangy/sour taste, and are used quite often in Indian curries, and cooking in other parts of (South East) Asia. 

Apart from mango powder (which is rich in citric acid, I use it as a replacement for lemon when I want sour, but no additional juices), I don't have any experience using them outside the realm of curries, so you'll have to experiment your way through them ;)