Note that Tesla's Web site asks you to log in to place an order. When they do so, the site seems to ping the car to find what charge port ECU is installed, and either enables or disables ordering depending on what's found. I've seen multiple reports from people who've done unofficial upgrades (even Gen3->Gen4 upgrades), and who
are able to order the adapter, even though their cars lacked CCS support from the factory. Thus,
@LBM4 and others with the de-CCS-ified Gen4 ECU won't be able to buy the part now, but if they do the ECU swap themselves, they should be able to order after the ECU swap is complete (including re-installing the car's firmware). It's conceivable there'll be some extra time lag in this, depending on whether Tesla pings cars as the store's Web page is accessed or on some sort of schedule.
Of course, the third-party clones and similar products are sold by stores without this ability. AFAIK, they'll sell to anybody.