Where can I find the Apple Diagnostics/Hardware Test tools online?

I have a MacBook Pro 13" Retina Display (Late 2012, A1425, "MacBookPro10,2") that is shutting down randomly. The fans are working but don't turn on automatically based on CPU temperature etc. so I have to set them manually to keep the system running. I've tried replacing the heat sink/thermal paste but the problem persists.

As long as I've been using Macs, though, I've NEVER known them to shut down due to thermal issues. In my experience they usually throttle themselves so that the temperatures go down, which suggests maybe there's an issue with the memory or similar, but I'm unable to run the Apple Diagnostics tools (holding 'D' on boot) because I guess the previous owner replaced the HDD and now it's missing the 'TestSupport.efi' that I guess is the diagnostics EFI partition or similar. I can't even load it via internet diagnostics, it just gives me the same error.

I figure I either need to rebuild the TestSupport.efi partition or download some other version of Apple's diagnostics tool or Appl Hardware Test tool myself, but I know Apple doesn't make that stuff publically available. I've managed to find some online repositories of their test tools that people have uploaded, but not the ones required for my specific hardware (A1425).

Does anyone know where to find (legally or otherwise) these tools or could point me in the right direction for restoring my previous TestSupport.efi?