What kind of anime girls with guns game are you looking for specifically?
There is a pretty wide gap between a game like Arknights or Endless Alice and a game like Gal*Gun or Senran Kagura Peach Beach Splash.
How old do you want the game to be? Is the strategy RPG Tuned Heart (1996) too old? Do the girls have to be the playable characters? What about genres, are Tower Defense or Bullet Hell games included?