trying to find a AKiTiO Thunder2 PCIe Box - or alternative
 

I'm looking try to find a AKiTiO Thunder2 PCIe Box to use some nvme storage over thunderbolt 2 on my mac pro 2013.

These appear to be long EOL and impossible to find, is there anywhere that is the go to place to get these or is there an alternative that's thunderbolt 2 or not insanely expensive like the sonnet version ?