I am not too sure about this. There is no company I trust to sell GrapheneOS-preinstalled phones other than GrapheneOS themselves.
Preinstalled GrapheneOS would be funded by state Honeypot operators, or potentially thieves or blackmailers.
If you wish to steal from someone, select from a population of thieves since they won't go to the police (although they may use illegal means to punish you).
Going with the stereotype that people doing illegal things prefer a secure OS (and are not smart enough to pick a safe source).
GrapheneOS is installed with their keys which you can verify, right?
You can verify the installation integrity via android attestation, which grapheneos uses
We are going to be reinstalling GrapheneOS on the phones shipping with it.