I filed for these documents under Air Force Instruction 10-206 OPREP 3, through the US FOIA.
These documents give indication as to the nature of the contents of such reports, you will find a designated letter after OPREP-3 which is important to give you the sensitive nature of the reports. There has been only one OPREP 3 document released pertaining to unidentified activity (UFO?). I do know since I have seen an official letter that there are OPREP 3 reports in the DOD concerning UFOs which are deemed "extremely sensitive." This was in the 1990s, so how many more reports have there been?
The first link is AFI 10-206; the second and third are the declassified OPREP 3 reports, and the forth is the unidentified (UFO?) OPREP 3.