I know that cornichons are a type of pickled gherkin. None of the grocery stores in my area carry them. Would the best substitute be miniature dill pickles, miniature sweet pickles, or something else? Or would it be something akin to miniature dill pickles with a certain spice added?
Sweet pickles, miniature if you're not dicing them, it doesn't matter if you are dicing them. Look for a bit of crunch; cornichons provide texture as well as flavor.