The botanical issue you raise is complicated by the linguistic quirk that the Spanish word for lemon, limón, is primarily used to refer to limes in Mexican Spanish (alongside the regular word for lime, lima). The large, fleshy lemons that grow in California and Florida are rare south of the border, in Mexico or anywhere in Latin America. Rick Bayless, author of several prominent Mexican cookbooks, says he has only seen our yellow lemons sold commercially in northwest Mexico, where they are called limónes reales.
Besides differing in size and color, US lemons also have a different taste and sugar content. One place where this is particularly evident is in the preparation of seviche, where you cure or “cook” raw fish in citrus juice. In many parts of Latin America, the stronger, more acidic lemons are used. But lemons in the US are sweeter and less acidic, so we generally use lime juice instead to cure the fish.
Lemons and lemon juice, which are staples in so many US recipes, are seldom used in Mexican cooking, where the lime reigns. Short of traveling to the northwest in search of limónes reales, you might also look for the limón dulce, which is actually a lime, but a sweet, mild one, and might be a reasonable substitute for US lemons.