We don't have a "native" Opera extension, however, it is possible to install TubeBuddy on Opera with this simple trick:
Step 1:
Go to the Chrome Web Store in the Opera browser - https://chromewebstore.google.com
Step 2:
Install TubeBuddy in Opera from the Chrome Store: https://chrome.google.com/webstore/detail/tubebuddy/mhkhmbddkmdggbhaaaodilponhnccicb
Done! That's it.
Bonus: you can now install ANY Chrome Extension on Opera in the future :)