Don't you have a simple needle or triangular file, it will work with some patience. You can also take the G file, put some sanding paper "around" and file the D string slot and so on. You can even use this old trick with a string a bit smaller "wrapped" in sanding paper to file any slot. Or you can buy the real deal. They are expensive, but worth every penny. These Ibanez nut files are excellent : https://m.thomann.de/gb/ibanez_4449eb6x_nut_file_set.htm?o=3&search=1611753350
And don't forget to clean your files very often.