You can get it here:
http://www.rnh.com/show_detail.asp?id=SM&s=1
And when you purchased the rights you should have been given a rental list which includes the full vocal scores and libretto for the cast.

Since I know you've purchased the rights...
here is the link to the rental eqipment from R&H.
http://www.rnh.com/show_detail.asp?id=SM&s=1.