I received these images from Christina Bowker.
My correspondent expressed surprise that a request would be sent by mail but I think this was very common in those days, perhaps more common than phoning in, although that would have been possible. Radio stations did not have the capability at that time to put phone calls on the air I don't think.
I was also asked if any recordings might exist from that era. I think that would be extremely unlikely. The only means of recording in those days would have been electrical transcription. I think very few individual stations had such capability and even if they did, it would be unlikely the disc, a large phonograph record, would have survived.
If Flagg continued in radio for some years, there may be a possibility of a recording of him from later.
My thanks to Christina for sharing this photo, one of only a few she has. I mis-filed the letter in my word processor and am happy that I finally found it.