Vocal selections I don't know, but I thought that you're only allowed to purchase or rent libretti if you're putting on the show. That was always my understanding.
The rain we knew is a thing of the past -
deep-delving, dark, deliberate you would say
browsing on spire and bogland; but today
our sky-blue slates are steaming in the sun,
our yachts tinkling and dancing in the bay
like racehorses. We contemplate at last
shining windows, a future forbidden to no one.
Derek Mahon
"Maybe all one can do is hope to end up with the right regrets."
Well the libretto of hairspray, Rent , Producers and Wicked have been realeased in those books all about the show. So the only way they would release the libretto is if they came out with one of those books.
The script will not be published (if there is no commerative book) until the rights are released for production, which will most like not happen for a few years.