To show bind mount source path for mount after v2.25.2

Have you considered using findmnt?

mount stores its information in /proc/mounts (or /proc/self/mounts), which is symlinked to /etc/mtab. mount will simply cat this file, and it no longer stores bind information.

What you can do is grep the /proc/self/mountinfo:

$ less /proc/self/mountinfo | grep /my/mount
221 84 8:3 /bind/source /my/mount rw,relatime shared:32 - ext4 /dev/sda3 rw,data=ordered