The American Airlines site mentions CareNow clinics as a place to get COVID tests in the Dallas area. They are not listed on the Trusted Traveller site, but AA says they can provide the necessary test:
www.aa.com
AA Also mentions the Lets-Get-Checked test:
https://www.letsgetchecked.com/us/en/american-airlines/, also not listed as a Trusted Partner.
I live near Austin, and we have CareNow clinics here too. However, they don't show up if you go through the
www.aa.com site. I still haven't been able to get an answer whether the clinics here would work. The local clinic says of course they can provide the test, but I'm not sure if it will be accepted.
So far, I'm intending to use Vault. I'll report back next week how it goes.