Salvadorans make up the third largest Hispanic group in the US so there are many places (at least in major metropolitan cities) that may have some of the authentic ingredients that you are looking for. I don't know of a Salvadoran dish that is "Americanize" we don't have a Tex-Mex equivalent here in the states.
​
One major distinction El Salvador has over Mexico is that Salvadoran cuisine is not spicy. You can add hot sauce if you wish but the dishes often don't include spice in them.
​
Amazon has a cookbook but I can't vouch for it because I've never read or own it.
The comments are positive though.
​
Good luck!
​