FYI, we will probably have to wait until July 1, 2023 for BYU/Big 12 cobranded merchandise to be available at retail. This date will be set by the Big 12 Conference and you can count on whenever that date will be, that it'll be very well publicized and a huge event built around it.
This is what was done with the other conferences when schools were added. They had to wait until they were official members of that conference.
So stay tuned for the big day!