Where can you find the FULL script of Sabina by Severino Montano?

The script of Severina is included in "Selected Plays of Severino Montano" which was published by the Cellar Book Shop in 1982. I don't think there is a current edition in print, so your best hope would be to look at sites such as Amazon, e-bay or secondhand book sites, some of which may have a search service.