Mice are neutral level 1 critters found in Westfall behind the inn or at the Jansen Stead amongst other locations [32, 52]. Also in Grizzly Hills e.g. with the pack of deer [20, 75] or near Voltarus [26, 50].
If you do not see any, try killing the other critters such as the snake behind the inn and see what re-spawns in its place. You may have to try a couple of times to get the mouse to spawn.
Try also, as they are fast runners, setting up a macro to:
- /Tar mouse
- /stopmacro [noexists]
- /cast Shoot
Replacing "Shoot" with your instant spell such as Moonfire