Purchased Toshiba RD-500 NVMe SSD. The SSD is now available from the mainboard. Am able to install OS on this drive.
However the Toshiba SSD Utility software can't get access to the disk information. CrystalDiskInfo doesn't display inforamtion about PCIe/NVMe version/generation. CrystalDiskMark displays 2 times lower read/write speeds than the specs posted on Toshiba's website.
Anyway I see no trouble in this since the stock SK Hynix NVMe ssd was showing lower operation speeds than the current one. Problem solved.