Lost and Found Achievement in Mass Effect 3
Lost and Found25
Dispatch 10 probes to retrieve people or resources in Reaper territory.
How to unlock Lost and Found
Once inside Reaper territory you can use to scan for resources. EDI will let you know if something has been found. Enter the planet's orbit that gets marked, to start the scan, then hold while you rotate the planet until a white light shows up. Then hit and launch a probe to retrieve the resource. Sometimes you will find things related to your sidequests. If you need to "find something", many times it's something you find while looking for resources.
Note: You may keep reloading your checkpoint after finding one if you want to get this achievement out of the way faster.