I'm looking to conduct a qualitative study involving art instruction in a school located within a community with high populations of migrant farmworkers.
The US DOE should have that data, or the states. Obviously Texas and California have high migrant populations, and the Southeastern US also has high migrant farming populations. You might consider contacting the USDA to see if they have data in this respect.
Also, you might look at the list of colleges that have CAMP (College Assistance for Migrants Program). Presumably, they would be in areas with high migrant populations, although not just Mexica-American.