The support, while being mostly useless, informed me that Pixels phones from them are always unlocked.
I thought this in my initial line of questioning, but when pushed, the support person had completely ignored the word "bootloader" (and surrounding context) and assumed I was referring to carrier-unlocking. When I pushed more, they realized what I meant, got in contact with technical staff, and started dissuading me from trying to "root the phone". Trying to explain that GrapheneOS uses verified boot did not help. In the end, they failed to give me an answer one way or the other, but when I purchased the phone, the bootloader for my Pixel 6a was unlockable.
But yes, phones sold from the Google Store, US or otherwise, likely all have bootloader unlocking available to customers.
As @JuTaRo says, the bootloader is always locked on Google Pixel phones, and it should be. GrapheneOS expects and strongly advises you to lock the bootloader (providing an easy button in the web installer that does so) after installing to maintain verified boot, and to satisfy checks from some financial apps such as those from banks which check if the bootloader is unlocked. Bootloader unlocking is the functionality we need, which is the ability for the customer to unlock the bootloader so they can install another operating system like GrapheneOS on it.