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.
Cervoz Lunches New M.2 2230(A&E key) NVMe PCIe Gen3x2 SSD
SK hynix HFM512GDHTNG-8310A 512GB MVMe PCIe Gen3x2 M.2 2242 SSD FOR T480 Laptop | eBay