Most of the ones I see on a google search available for sale are from UK or CND hearing product resellers. I also have a Roger On and wish to have more cables…
All of the cables I saw on amazon and ebay appear to be oriented toward pulling audio from a phone (and into an aux port or headphone) as opposed to squirting audio into the mic.
If you find a source, report back, it would be helpful to know!
WH