The Trijicon might still use US Glass from NY, the prototypes were US sourced and they might have continued that, but remember the US Glass companies are still foreign, they just have offices here. Most of it is small batches for prototyping.
US Glass is a complete non-issue... there is not a single camera lens that is held in high regard because it is made here. Quite the opposite in fact. The issue is, how much the companies are willing to pay and what grade they spec. Most try to balance cost vs return, so you have everyone on a pretty level playing field, but there is certainly better glass available. At the end of the day it is more about the quality of the coatings and not the glass itself. The process to apply the coatings, the spec on the mix and how well they hold up over time. (Sunlight kills lesser quality coatings)
Spotters, cameras, etc, all have great glass, none of it sourced here.