Rocket League McLaren DLC?

I want this rocket league mcLaren DLC, but don't know how to buy it today (PS4).

You can't anymore, because the DLCs have not been available for a long time. But Psyonix said that old DLCs might find their way into the item shop at some point, so unfortunately you have no choice but to hope that it will come to the item shop at some point, if you really want it.

Rocket League® - McLaren 570S Car Pack is currently not available.

https://www.microsoft.com/...verviewtab

Unfortunately, it is currently not available for purchase.