What kind of sour/unripe fruits can you easily find in the USA?

One of my biggest food cravings that seems to always go unsatisfied unless I'm in Asia is buying sour fruit (like star fruit) or unripe versions of sweet fruits (like unripe mangos) and eating it with spicy salt.

It seems like Americans just don't have a taste for sour fruits and I haven't been able to find any of the sour fruits I'm familiar with at the grocery store. Does anyone have any suggestions?