I'd like to upgrade my custom EliteBook 8770w to have a Radeon RX 580/580X Mobile. According to the TechPowerUp GPU Database, such cards do exist (For some reason, the given specs of the 580 and 580X are the same). However, I haven't been able to find one for sale anywhere; I only get search results for the desktop version.
Could someone explain what's going on here? Maybe it's only available for OEMs and isn't sold separately?