GM, Ford, GE, Johnson & Johnson, Nike, 3M, Eli Lilly, Cummins, ... I could keep going. Maybe not all have it to the same degree as Apple, but are sufficient to make a face shield.
Lot's of companies could do this. I'm glad Apple is giving it a go.
The US is an extremely massive manufacturing nation. There are dozens of companies in the US that could mass produce these face shields. It's great that Apple moved quickly to do it, it's certainly in their wheelhouse to make happen.
These shields are easy to manufacture. They're ideal to rapidly produce, cheaply and at scale. Compared to normal shields in the industry they're no-frills, which is perfectly fine, as right now we just need volume.