Just type: label:[LABEL]
Without the square brackets, of course. Example: Universal
I just learned about this feature in this thread. As you reported, I get only a few results for "Morr Music", but I get a lot more searching for "Morr". Maybe that will give you what you want.
A note to others having problems with this: I wasn't getting the results I wanted in the desktop search until i realized that there shouldn't be a space between the colon and the label name - label:steeplechase instead of label: steeplechase.
This is a great feature!