can i use state resist in class parameters for this?
State resist does not stop you from using a skill on a battler. It just stops the state from happening. So that would be pretty annoying to a player to use the skill and it just wastes their turn.
As Andar said, Yanfly's Selection, while not free, is the way to do this (I don't know if anyone has written a free equivalent).
You would put this as the notetag in the skill's notes:
Code:
<Custom Select Condition>
condition=target.isWtypeEquipped(X) || target.isWtypeEquipped(Y) || target.isWtypeEquipped(Z);
</Custom Select Condition>
where X, Y and Z are the weapon types from the Types tab that you want the skill to be usable on. You can add as many as you like, following that format.