"Thank you for your inquiry regarding the importation of musical instruments with abalone shell from New Zealand that will require clearance by the U.S. Fish and Wildlife Service. Our mission is, working with others, to conserve, protect and enhance fish, wildlife, and plants and their habitats for the continuing benefit of the American people.
The U.S. importer is responsible for the legal importation of these musical instruments with abalone shell from New Zealand.
If the U.S. importer intends to import these musical instruments for commercial purposes, consistent with our definition of commercial, regulations contained in Title 50, of the Code of Federal Regulations, Part 14.91, require that they must obtain an import/export license prior to engaging in business as an importer or exporter of wildlife or wildlife products. The license is valid for one year from the date of issuance and costs $100.00. In addition, as an import/export license holder, the U.S. importer must pay inspection fees for each wildlife shipment imported or exported under the license. For information on inspection fees and how to calculate the inspection fees that the U.S. importer will be required to pay, they can visit our website at:http://www.fws.gov/le/AboutLE/2010InspectionFees.htm
Any wildlife shipment would be considered commercial if the shipment is being imported or exported " related to the offering for sale or resale, purchase, trade, barter, or the actual or intended transfer in the pursuit of gain or profit, of any item of wildlife and includes the use of any wildlife article as an exhibit for the purpose of soliciting sales."
So, looks like if you are sending a musical instrument to a customer for his own personal use then there is no problem. But if you are sending it to a shop for resale then the shop needs to get an import permit (cost $100), get the shipment inspected, and pay the inspection fees. That is a significant incentive not to send to a US based shop! All this for shell that probably cost less than $30 and weighs a few grams. That really is going to stop illegal poaching of Paua in NZ.

Peter