Back when I was riding I used to use a Blackhawk Sahara Strider. Unfortunately they stopped making them but it was a chest rig that allowed you to conceal a handgun (a bit cumbersome to draw from) and other gear that you may need. I used to carry a Glock 26 in mine but it would fit probably up to a 19 or 17.

When I stopped riding because I got lazy and was told I had to stay out of the sun so much I gave it to a friend. Not sure if he still has it but I will ask and let you know if he is not using it and you could check it out.

In the alternative you might take a look at the 2A holsters website. They have some chest rigs that I have seen in action and they seem to work pretty well. A guy I know uses one to carry a full size handgun when he runs.