I see no subject complement in this sentence.
Here's how I parse it:
The subject of the main clause is This instruction. (This, by the way, is an odd expression: an instruction is ordinarily a single directive, not a document containing a number of directives.)
The verb in the main clause is provides.
The direct object of provides is noun phrase the rules for sharing information originated by the Purchasing Department. That noun phrase is composed of
- a determiner, the
- a noun, rules
a preposition phrase, for sharing information, which acts as a complement of rules.
(Note that this is not a complement of the verb provides; for in this case is selected by rules to introduce the matter which rules concerns. The for PP as a complement of provide would have a quite different meaning, approximately "to assure that information is shared".)
a passive participle phrase†, originated by the Purchasing Department. The participle-plus-agent-complement acts here as a modifier—an 'adjective' in traditional grammar. We usually call the noun which a modifier describes its head (an adjective or PP in predicative position describes its predicand),‡ not its subject.
In this case the head of originated by the Purchasing Department is ambiguous: the 'default' reading by position is that it modifies the closest nominal, information; but in practice careful writing cannot be assumed, so it may be intended to modify rules.
† Some grammars would parse this as a "reduced relative clause"—that is, a relative clause from which the relativizer and copula have been deleted:
which BE originated by the Purchasing Department.
‡ To tell the truth, I dislike both these terms; head is inconsistently employed, and predicand is sometimes used in ways which obscure the fundamental difference between a modifier and a predicate. I know of no term for the entity which an adjective or 'adjectival' phrase describes regardless of syntactic position.