Dear Mr. Schneider,
Thank you for posting your request on History Hub!
We searched the Air Force History Index and located 10 records pertaining to 91st Air Defense Group (ADG) and 17 records pertaining to the 91st Air Defense Squadron. Please read the brief Abstract to determine which records you are interested in and click on the specific PDF icon. In the PDF listing, the IRISREF is the microfilm reel number and note the FRAME and FRAMELST numbers for the location on the reel. If the reel number begins with A, B or C, please contact the National Archives at College Park - Textual reference (RDT2) via email at firstname.lastname@example.org for access to them.
If the reel number begins with D - Z, the microfilm is still security classified and RDT2 will not be able to make the reel available to you. The original paper copy from which the film was created is still in the custody of the Air Force Historical Research Agency (AFHRA) and has been declassified as will be any general orders or unit histories of the units not included on the microfilm. For access to these records, please contact AFHRA, 600 Chennault Circle, Building 1405, Maxwell Air Force Base, AL 36112-6424. The web site is https://www.afhra.af.mil/.
We hope this information is helpful. Best of luck on your research!