Plan your purchase of Balinese silver to keep it within U.S. Customs limitations. In 2009, the normal duty free import limit was $800 for individuals. Since you are importing precious metals, keep your receipt so that you can prove its value if you are stopped for a customs inspection.
Travel to the village of Celuk, about six miles northeast of Bali's major city of Denpasar. This is the major center for gold and silversmiths in Bali.
Inquire about sheet silver at the artisan shops in Celuk. No one will actually be selling sheet silver, but some craftsman might have some on hand for a job they are doing and be willing to part with it. Alternately, you may be able to engage a silversmith to make sheet silver for you.
Travel on to Ubud if your scrounging in Celuk has not worked out. The villages on Ubud's southern fringe are home to a variety of workshops. There are almost as many silversmiths here as in Celuk, although they are spread out over a much larger area. Repeat your inquiries from Step 3 here.