This is a fairly dumb question, but are these not Mexican? I just spent a fruitless hour looking through all the menus for taquerias in Washington Heights/Inwood, and none of them have them. Even the places with words like 'Baja' and 'California' in their names. Are these strictly an all-the-way-downtown food?
Is the cuisine of Puebla/Guerreo/Oaxaca not Mexican? I feel your pain but as a former resident of South Tucson and East LA I have learned to embrace tortas and cemitas along with assorted moles and caldos I never enjoyed before. For example, Tacos Matamoros down in Sunset Park has an excellent fried fish torta that is often a special... maybe you can find something similar in your hood.
But yeah, La Esquina downtown if you must... bring a fat wallet.
if you dont want to treck downtown, Gabriella's on the UWS (93rd and Columbus) has very good fish tacos (also have shrimp tacos).
Oh, they are definitely Mexican. Maybe there is just not that much demand for fish in those areas of town? Or maybe its more difficult to store or more expensive (a good fish taco needs to be fresh fresh fresh, which is why I assume I'm not seeing them at the taco trucks). Or maybe the Mexicans who move to NY and open taquerias aren't from the Yucatan/Veracruz/other coastal areas and prefer to make more northern mexican specialties?
I had some tasty fish tacos at Pinche Taqueria in Nolita not too long ago. And here's a review of some more (nothing uptown):
I've enjoyed fish tacos at Dos Caminos in Manhattan. I don't know that they are still on the menu, but I think they probably are.