Online text:

Volume 1 and 2 (1754): GOOGLE BOOKS

Volume 3 (1755): GOOGLE BOOKS

Volume 4 (1758): GOOGLE BOOKS

LATER EDITION:
Published in Gotthold Ephraim Lessings sämmtliche Schriften, edited by K. Lachmann, Berlin, Voss, 1838, vol. 4.
Online text: GOOGLE BOOKS

RECENT EDITIONS:
Published in Lessings Werke, collection of works by Lessing in 25 volumes edited by Julius Petersen and Waldemar von Olshausen in collaboration with Karl Borinski (Berlin, Bong, 1925). The collection includes an introduction and the annotations by the two editors and a complete index of Lessing's works.

Anastatic reprint: Werke. Vollständige Ausgabe in fünfundzwanzig Teilen, Hildesheim, Olms, 1970. The Theatralische Bibliothek is contained in volume 6, 43-45, in volume 10, 115-483 and in volume 11, 37-453.