Years ago I searched and searched, found listings but none in stock. I bought a "shaft coupler" and made one. Not in a position to take pics, and the ones I did take died with my old computer. (back-up back-up back-up...) As I remember, the set screw was in the wrong place so I had to cut a little off the end, then cut off the piece I needed, then drilled two 5/8" holes because I had no easy way to cut slots and I thought holes would be stronger. Can't remember it being that difficult, but it was a while back...
Here is a link to a picture of a coupler
https://thebigbearingstore.com/1-3-8-shaft-coupler-with-keyway/