I have seen photos of a shelf on a C14. Might have been police, at that.
It was, but most could fabricate their own. It's just a piece of sheet metal with three tabs attached to the bike with well nuts.
I had to buttress support mine, but I'm putting considerably more load on mine. For just a radar detector the 3 tabs should be enough support.
It appears to be made from 16 gauge steel. Mine measures .065" thick including the paint on both sides. I think that if additional support
was desired for a light load that a curved support made of foam/plastic/wood that rests on the curved top of the speedo/tach unit would suffice.
It also is nice shade visor for the gauges as well.
https://fartymarty.smugmug.com/Motorcycles/C14-Dash-Shelf/n-H7d8LF/