I asked Jake Croston (The Big Chef), what I could use for a replacement for citrus. Check him out! He said:
You can easily replace the acid flavor in the citrus with a light vinegar like a rice wine vinegar. now the conundrum comes when you want the lemon flavor!!
You have a couple options however! For the lemon, you can use either lemongrass, or lemon balm! The lemongrass you will have to pound out a bit, slice it, and blanch in the vinegar. Then let it sit in the refrigerator for a night or so.
The lemon balm you can rough chop a bit and do the same. You don't want to cook it for a long time, just until the color comes out into the leaves. Then cool down, let sit overnight!
For the lime flavor, you can use lime balm, lemon balm's close relative. Or you can use lime basil, and that will add that flavor in as well! Use the same technique as the lemon balm.
This way you can get the flavor of the lemon and lime, and the acidity!
I hope this helps!