As of this writing, one of the safest public sources is the bundle hosted on archives like firmwarefile.com or gsmdevelopers.com . Look for a package named:
Restart your PC. Test Mode will appear on the desktop—this is normal. spd flash tool r4.0.0001 download
Always run the downloaded file through VirusTotal before execution. A few heuristic detections are normal for flashing tools (as they interact with hardware), but dozens of alerts signal a real threat. As of this writing, one of the safest