Possibly your best first try would be search.usa.gov to look for state as well as federal reports and websites. But their plain Bing search, like Google, does not allow very precise searching. The search for both exact phrases: "undocumented immigrants" "diabetes statistics" is TOO restrictive, and gets only 2 hits; "undocumented immigrants" diabetes statistics gets 6330. That DOES, however, drop to about 153 as you scroll down to see more hits - not an impossible number to look at. Compare Google's search for: "undocumented immigrants" diabetes statistics site:gov ("about 2300 results"), which turns out to be 435 "unique" hits on 44 pages. No doubt it's best to first look at the 8 hits for: "undocumented immigrants" "diabetes statistics" site:gov or the "18" (really 13) for: "undocumented immigrants" "diabetes statistics" site:edu - though you might well be missing some good pages that don't have those exact phrases.
Google Scholar can quickly get frustrating unless you are going through a large university's proxy login - to get access to its large number of commercial journal articles. It gets 10 hits for: "undocumented immigrants" "diabetes statistics", and a few seem to be free online. But its "about 1040" results for: "undocumented immigrants" diabetes statistics may well be that many, and they look like primarily commercial journal articles.
