I think there is an implementation of Maybe (and perhaps bind) here: GitHub - miguel-negrao/FPLib: Functional Programming library for SuperCollider
I think it’s called Option:
EDIT: just to be clear, the type constructor Maybe is just one kind of Monad, it’s often given as an example because of its simplicity. It makes sense to take a look at languages like F# and Scala if one wants to have a more idiomatic syntax in sc. Also, they avoid these mathematical terms like “monad” that can sound scary sometimes.