He sent half a power module?
EBay will refund you.

Welll. If you can get an STL and you wont, you can get it printed at many online places like PCBway in aluminium or stainless steel...
I am awaiting a delivery of a metal 3D printed part right now! Plastic isnt really good enough for that as its a part of its heat sink. You could pot in in epoxy...
Mine all have backs...