XPS 8960, Dell OEM video card upgrade?

I have an XPS 8960 with a 1000 watt PSU and an Intel Arc A770 video card. I'd like to change it to an RTX 4070 or similar. 

Looking on the Dell site, there does not appear to be any ability to buy a new card - the XPS 8960 didn't show up in the upgrades and parts area and I'd rather not have to fiddle with secure boot to install a retail card if I can avoid it. 

Any ideas on how to purchase an OEM version of an Nvidia card?