You can spend a pile of rubles and pay to the dealer, or you the use your head and figure out *something*.
A mirror attached on the plastics would *not* work -- vibration would make it useless.
Option: drill out whatever is in the mount, use an "easy-out" to unscrew that whatever, and mount a mirror.
If the hole in the mirror mount is deep enough -- JB Weld into the hole, put a mirror in, let is dry for 3 days.
FYI, makers matter. I rented a Vespa LX, it had a none Piaggio mirror on the left that was useless at speed because the vibration. Piaggio mirrors are heavier to not vibrate.