Finding LAWs is up to RNG since bonus areas don't exist anymore and we can only spawn them after AW battles. The only thing that increases the spawn rate is if you have one of the divine priest jobs in your alliance

You can always leave the FAW alive and increase your odds solely on the fact that you'll be saving BP for more potential LAW encounters instead of killing FAWs and lowering your chances by limited your BP.

You're welcome and good luck ^^