I harvested a PCIe Gen3 x2 NVMe 1.3 SSD from my older laptop, the problem is that its length is short. I've held it in place with some tape, it should hold.
Western Digital SDAPMUW-512G 512GB PC SN520 PCIe Gen3 x2 NVMe V1.3 M.2 2242 Internal Solid State Drive - Newegg.com
960GB Transcend JetDrive 820 PCIe Gen 3 x2 SSD for Select MacBook Air, MacBook Pro, Mac Pro
Amazon.com: PCIe Gen3 x2 USB 3.2 / 3.1 Card ASM3142- PCI Express to 4-Port Type C HUB Internal Expansion Card Controller Adapter PCI Express Card Desktop PC Support Multiple INs : Electronics