Apple AMD Radeon Pro 580X Graphics Card MPX Module for Mac Pro (2019)

you are not talking to Apple when you post here. Readers are other users like you.

Rx580 MPX modules do not appear to be available for sale as new direct from Apple, but they are available on the used market

here is an example:

https://eshop.macsales.com/item/Apple/VM2019R580XU/

you may be able to find it locally.