There are some phones sold with /e/os, but I doubt they'll ever be sold in any kind of brick'n'mortar in the US, let alone by any of the major carriers.
iodé also sell phones with different OS in the EU.
I purchased a Shift6mq from them because Shiftphones do not ship to UK and got it with iodéOS installed on it and bootloader was locked and it still booted up and worked. So at least in the EU it is possible to ship phone with alternative OS with locked bootlaoder.
