You could experiment with trying to get those other frequencies but I doubt you will have much success with your 36" dish AND it would involve buying a C-Band LNBF and the proper feedhorn. Not worth it for an "iffy" reception of maybe one transponder in the entire arc.
You could put in 11760 H 30000 and 11880 H 30000 and scan each but why not just go to the "scan single satellite" then pick 103 W and in the "scan mode" section change it to blind scan. Let the receiver do the work for you. I hope you are peaked for the strongest reception as 11880 is a little weaker.
Did you mark the pole where you were first when you discovered the Mexican channels? If so, and you are on 103 now you know that 91 is in between and so is the elevation adjustment. Mark where you are before you move again so you can always go back. You mentioned Antenna TV and that is on 91 but could be taken off at any time. COZI is an acceptable option and has been there for years.