HeinOnline's American Law Institute Library has the most comprehensive collection of drafts for the Restatements of the Law.
Restatement, Third, Restitution and Unjust Enrichment (1998-present)
Restatement, Second, Restitution (1981-1984)
Restatement of the Law, Restitution (1933-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* Restitution for a full list of available drafts.