Where to find Garrison Defense Strength for City-States?

[Das Capitolin]

When playing against AI at advanced difficulty, I find that City-States are almost immediately wiped out by civilizations with 5x the strength. To remedy this, I would like to make the Garrison Defense Strength stronger than the other AI so they can survive the game. Perhaps a modifier value can be changed, or I can give City-States outer walls early. Can anybody point me in the right direction?

 

[Das Capitolin]

After exhaustive searching through xml files, I couldn't find a way to manipulate Garrison Defense Strength for City-States. I did, however, find plenty of mods that can help keep them alive in extremely difficult AI games:

Tougher City States
TCS Free Walls for City-States
CIVITAS City-States Expanded