I've seen it written this way a couple of times, e.g. in oxford entry for dame: 'There's must be a wealthy society dame (preferably played by Margaret Dumont) who is entirely smitten with Groucho, though he walks all over her'.
What does the phrase mean / how is it different from just 'there must be'?
And BTW what does 'there's' mean in such a phrase? Is it 'there is' or 'there has' or?..