As mentioned, lemon juice or lime juice or if you want it dry, "True Lime or Lemon".
https://www.amazon.com/True-Lime-Sha.../dp/B001Z2O0T4
There are a couple of alternatives that I've come across.
Citric Acid is available in the spice aisle, I like to add it to my Guacamole, it adds a nice flavor and preserves the color.
Sumac is another one, harder to find that adds a nice citrus taste.
Depending on the dish, some type of vinegar may also work.