You should be able to find the rule based on what law the court is stating as reason for the case. I don't know how the cases are presented, but either you google for law databases (might have to search for local laws depending on where the case is). I'm pretty sure most cases will give you the statute/bill that is the reason for the case, but maybe that's because I've only looked at case summaries for some ethics projects.
EDIT: For example, on this page:
[FN 3] The original complaint alleged the following causes of action: (1) unfair competition (Bus. & Prof.Code, § 17200 et seq.); (2) false advertising (Bus. & Prof.Code, § 17500 et seq.); (3) libel; (4) slander per se; (5) violation of the Lanham Act (15 U.S.C. § 1125a); (6) violation of Penal Code section 637.1; (7) invasion of privacy — false light; (8) invasion of privacy — appropriation of name; and (9) conspiracy.
[FN 4] These causes of action included: (1) unfair competition (Bus. & Prof.Code, § 17200 et seq.); (2) false advertising (Bus. & Prof.Code, § 17500 et seq.); (3) libel; (4) invasion of privacy — false light; (5) invasion of privacy — appropriation of name; (6) conspiracy; and (7) breach of contract.
The rules would be from the bill or whatever Bus. & Prof.Code, § 17500. Cite specific language from the bill/law.