Are these very rare? Anyone know the best place to find them?
Zombie mushrooms are pretty easy and drop both. Pigs supposedly drop one or the other but yes they are pretty rare. =/
Green mushrooms drop them as well. That is where Kemwek found his S.
Anything that drops other letters, drop the M and S.
I got an M and an S from slime tree >_> Sold both for 670k...