In the past, some have been asking about a single earphone to use in their scanner. CCrane has one available at a relatively reasonable price. It has a stereo plug and combines the signal into one earphone. I haven't bought one yet but CCrane is a reputable company. Below is a link:
CC Buds Solo In-Ear Single Earbud for Radio, Audio Books and Podcasts
Single Earbud, great for podcast listening, exercise and listening to the police scanner. Tuned for superior voice clarity with a 1/8th inch standard stereo to mono auxiliary cord.
ccrane.com