Allergic to lemon

A warning about using lemon verbena tea as a substitute as it can cause some people to be photo sensitive and react badly to sun exposure. It happened to me (red, swollen, itchy face) and when I looked into the probable cause it turned out to be lemon verbena I had steeped for tea.

lemongrass puree [fyi, lemongrass is a grass, not a fruit.] can be found in asian markets, both in its fresh grass stalk form and as a frozen puree. mango, passionfruit, both very acidic., all available as easy-to-use frozen purees.
p.s. have you followed the golden rule here?(SEARCH IN GOOGLE) for Lemon substitutes

In addition to the previous good suggestions, a few more ideas.
Keep in mind that when using a replacement or alternate ingredient your dishes won't taste exactly the same, or need the same volume specified for lemon juice (sometimes more, sometimes less).
In practice, start with a smaller amount of the substitute ingredient & taste. If more is needed, add. (Always easier to add than compensate for too much.)
Use odds and ends of wine, left open but undrunk after a meal.
Use other fruits that are not in the citrus family, but are highly acidic.
Play with flavors and textures: use a combination of solid, chopped &/or juices from these fruits.
https://www.healthline.com/health/acid-foods-to-avoid

Depending on the dish, you might use sumac or lemon verbena. Those both have a rather lemon like taste as well. Lemon verbena can be steeped in liquid to diffuse the flavor, for teas and even puddings. The flowers are really pretty, and make a nice garnish as well. Sumac has a reddish hue, so it might stick out a bit much, but it has a nice tart flavor and does well in dressings and seasoning mixtures. I like it sprinkled over salads, especially over Caprese style salads, tabbouleh and other grain salads, and fish.

For recipes that call for lemon juice as a garnish you can just swap in another acid- for fish dishes a bit of lime juice (if that works for you?) or for soups and sauces a bit of vinegar, red wine vinegar or even basalmic vinegar.
For salads that use lemon juice in the dressing white wine vinegar or red wine vinegar are good basics to use