A Colt factory letter has been ordered but it may not offer any leads. The historian thought that it would likely letter to the U.S. Government without identifying an individual.If you want to spend the $$ you can always get hold of Colt and ask them who the General was who received the pistol in question.
I certainly remember reading about your relative. Lt. General Buckner was KIA in combat on Okinawa. He died serving his country, God Bless.There are two books that might help you in your search for information. One is "The Colt U.S. General Officer's Pistol" by Horace Greely IV (1989 by Andew Mobray Publishers). The other is John Brunner's "The Colt Pocket Hammerless Automatic Pistols II" (2009, Phillips Publications). They both contain some serial number listings. Brunner's book has two listings: pistol serial numbers with dates and names and names with pistol serial numbers. An relative of mine, LTG Simon Bolivar Buckner, Jr., is listed in the name index but only the caliber is shown, no serial number.
Good luck in your search.