Must be nearly there with the 'oldies' now Rocker. lol They still bring a smile every time I hear them, as I am sure they do to all who have contributed.
Ah well! You can actually buy replacement bubbles, but they are encapsulated in a glass vial, so strictly speaking you are not buying just the bubble. lol
Another even simpler method is to 'jack out' the insert using a 'long enough' bolt, a large flat washer (bigger than the handlebar O/D) and a nut. 1) Screw a nut up the bolt thread 2) Fit the washer onto the bolt 3) Screw the bolt fully into the insert 4) Tighten the nut slowly against the washer which should 'jack out' the insert.
I just drilled the holes out with a 7mm drill and ran a M8 through the hole and then used the bolts which came with the mirrors.