To answer your question, there are no rules or laws that specially address what an acceptable percentage of recycled content is for decorative hardware, either from the manufacturing or the specification perspective (if you are looking for certification points).
In general, the higher the level of recycled content, the better, but this statement should be tempered by considering what the source of the recycled content is and what it takes to collect, transport and process that material. Sometimes the benefit of recycled content over virgin material is rendered valueless because of the high embodied energy of some recycled materials.
With respect to environmental product claims, the Federal Trade Commission (FTC) is cracking down on bogus claims, i.e., "greenwashing," with respect to how manufacturers can label products with perceived environmental attributes, including recycled content and recyclability.
The new Green Guides are expected to be published this spring, but in the interim you can reference two FTC brochures: "Sorting out 'Green' Advertising Claims" and "Eco-Speak: A User's Guide to the Language of Recycling."
Rather than looking for recycled-content hardware pieces, consider salvaged pieces. Depending on the style of architecture you are working with, you can often find salvaged hardware at resale stores and online at sites like Craigslist. It is generally considered more environmentally responsible to reuse an existing item rather than to purchase new, even when it has recycled content in it.
If you are a creative type, you can repurpose one thing to become another. For example, silver utensils found in antique and secondhand stores can be refashioned into robe hooks. Open-ended wall-mounted magazine racks can become toilet paper roll holders.
If you are considering marketing a line of recycled-content decorative hardware, you may want to confer with the Decorative Plumbing and Hardware Association. I am currently not aware of any product labeling requirements established for their member firms' products, but that is not to say they don't exist.