Adding values from a Map to an existing Source in Scala

I am using akka streams. Can we add values from a map to an existing source in scala? I want to merge all the values from a Future[Map[String, A]] and a source of A Source[A,_] which are not already in the source. My method signature is:

case class A(id: String, someValue: String)
def addValuesToExistingSource(mySource: Source[A,_], myMapFuture: Future[Map[String, A]]): Source[A, _] = {
..//This is to be implemented
}

Thanks.