HeinOnline's American Law Institute Library has the most comprehensive collection of drafts for the Restatements of the Law.
Restatement, Third, Agency (1997-present)
Restatement, Second, Agency (1953-present)
Restatement of the Law, Agency (1925-present)
Westlaw, available on the library's Westlaw computers, also includes select drafts for the Restatements of the Law.
Jenkins has select drafts in print and on micro in the library. Search the Jenkins' catalog for Restatement* Draft* Agency for a full list of available drafts.