Yep. Tortitas de camaron are pretty easy to find during Lent and tend to be made with ground up dry shrimp. I've seen it most often fried in little pucks, sort of like mini egg foo young patties, and sometimes placed in tortillas for tacos. As Rob says, they are usually pretty perfunctory and bad.
I want to emphasize what I noted above, though: pambazo is a type of bread first -- from "pan baso" which means essentially cheap bread.
Teleras are often substituted for
pambazos and they do a good job. I also wouldn't say that
teleras are more commonly used than
bolillos in
tortas around here.
Bolillos are more commonly used, though almost any bakery selling
bolillos also sells
teleras. I also wouldn't assume
pambazos (the rolls) are unavailable. Mexican bakeries are pretty good about special orders and I'd bet a place like Markellos might have them.
Cemitas, for example, which of course are elemental to the sandwiches at Cemitas Puebla, are more unusual than pambazos in my unscientific observations.
Last, while
tortas ahogadas and
pambazos can and do have any number of ingredients, the orthodox versions of these sandwiches have specific fillings on their home turf. It's
chorizo con papas for
pambazos in Michoacan as I understand it.