BI4IVM
I am not BY1BY OP.
However, as far as I know, their PO Box and QRZ.com page has already been set up.
You can simply send an email to that address and receive a reply.
However, I'm not sure if they support exchanging cards that are not QSLs (e.g., via HamCQ). I can send them an email to inquire about this.