mousses_rockets_0d Is there a boot loader unlock workaround?
None known, and unlikely.
If you want to run GrapheneOS in the U.S., the most-reliable way is a non-carrier-specific device straight from the Google store. Next most reliable is probably Best Buy.
There will be many ways to get a cheaper Pixel, but many of those devices can't run GrapheneOS. If you can see that the device's "OEM unlock" toggle is on, fine, but the seller using the word "unlocked" just is not a guarantee.