There are Proffesional Photographers that specialize in small items and jewelry. You would be able to contact those near you at a local Photographer's Association (use the Yellow Pages) or get information from your local professional processing developing lab (go to higher levels, don't stay with the lower employees). You may also try with a local Advertising Agency.
There are special cameras and setups for taking proffesional photos of jewelry (for Inventory purpose) that are used as part of a Jewelry Management Integrated Solution, you may try such an option. Maybe a local jeweler will have one of these and allow you to use it.
I would also contact people that are known for their work on pearls: Fred Ward or David Doubilet.
Happy Hunting!
Douglas