You can buy some paua abalone and either cut out the shape or there is a supplier that has many different designs as well as shell blanks www.luthiersupply.com . Look under individual shapes. If they are not too wide you can glue them to tubes, cast around them and turn. If wide, glue several together and with a round file or sand paper glued to a spare tube and make a contour on the back side that will be the same shape as the tube. There are a few of these in my album. If you want to just try this out an only need one piece of abalone to cut out, send me a pm.