Are any corn products in the United States made from nixtamalized corn?
Masa Harina is nixtamalized corn flour, as is anything made from it.  So, most corn tortillas you can buy are, as are premade tamales, sopes, etc.  While you may come across varieties made from non-treated corn flour (be suspicious of anything bright yellow), most are treated.  Corn/tortilla chips are a little bit more of a mixed bag; some are made from corn flour and some from masa, and it's pretty hard to tell from the labeling which is which.
Hominy is also nixtamalized, as are grits, and any product made from/with grits (no, grits and polenta are not the same thing).  There's another kind of masa, called masarepa, which is used to make arepas.  This isn't an exhaustive list, but should be sufficient to show that yes, we are eating nixtamalized corn in the United States.