The last original writ was issued on 2 June 1980.
See Chapter 5 of Baker's Introduction to the history of English law (4th ed 2002) for introduction, then his introduction to 94 SS (Reports of Sir John Spelman v.2) Holders of an Oxford SSO can access the latter online via HeinOnline.
Subject search terms to use in SOLO to find early printed works:
Pleading -- Early works to 1800
Actions and defenses -- Early works to 1800
Introduction to English Legal History by 
The Forms of Action at Common Law by 
History of the Common Law of Contract : the rise of the action of assumpsit by