I do not have a modified clayff.frc for other minerals because I am not using CLAFF.
I just let him (Sen Wang) how to make msi2lmp.exe working correctly. Unfortunately, I do not know the correct parameters for clayff.frc.
You need to search, find or simulate them.
However, if you want to use some parameters from other force fields such as cvff, pcff, you can take a look at cvff.frc and pcff.frc.
Then, you put those parameters into the clayff.frc. msi2lmp should work.