NVMe is just 4 lanes of PCIe.
Any 10$ PCIe to m.2 adapter will do.

Yes any NVMe to PCIe card would work but to boot off it I believe it need to be the HP one. They do a single NMVe turbo card as well if you only want a boot NVMe

Alas the site was in the U.S. I'm in Canada so it turned out to be very expensive.  The search continue.

FYI they were 4050$ and 5070$ Us Dollars respectively.

Fazz Powell:

20% vat-ouch.

One's view on this depends on one's value judgement of collectivism vs. individualism.
From a psycholocial standpoint I'm tempted to believe that collectivism represents a higher degree of integration of psychological functioning. But that's very speculative.

Pat Horridge:

Yes any NVMe to PCIe card would work but to boot off it I believe it need to be the HP one.

This should only depend on the BIOS of the computer.
When this C612 chipset came out, booting from PCIe wasn't supported, was added later.
Also possible that in this case HP was able to implement vendor lock-in, idk.

I'm tempted to believe that collectivism represents a higher degree of integration of psychological functioning. But that's very speculative.

I agree as well, I don't understand the Europes tax system. But I've put plenty into the pot for "the common good" :) 

This should only depend on the BIOS of the computer.
When this C612 chipset came out, booting from PCIe wasn't supported, was added later.
Also possible that in this case HP was able to implement vendor lock-in, idk.

H=ow can you find out your chip-set?

Fazz Powell:

I agree as well, I don't understand the Europes tax system. But I've put plenty into the pot for "the common good" :) 

by the same token, south-east asia should be the most mature.
Otoh western individualism replaced narcissistic god-kings with democracy, so who knows...

Fazz Powell:

H=ow can you find out your chip-set?

Googling the name of your processor + the term "chipset".
Or in device manager, is a bit messy, under "system devices", stars with a C, like C600, C612, C621...