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.
Corsair Force Series MP300 120GB M.2 PCIe 3.0 x2 NVMe 3D TLC NAND Internal Solid State Drive (SSD) | CSSD-F120GBMP300 Buy, Best Price in Oman, Muscat, Salalah
GIGABYTE、PCIe 3.0のM.2 NVMe SSD 2モデル - PC Watch
GIGABYTE M.2 PCIe SSD 512GB Key Features | SSD - GIGABYTE Global