I found the original design in a catalog, then used shapeways https://www.shapeways.com/creator/2dto3d#landing to generate a .x3db file (Shapeways .x3db to .stl?) NOTE – Must use Chrome browser IE does not work.

Then I used Netfabb basic to convert the file to stl. netfabb Basic Netfabb is free.
To export  (part >> Export part >> as STL)

I opened the STL in 123d Design and used the Spline tool to trace the outline of the shape I wanted. Once the shape was closed at the ends, I extruded the flat surface up 3/8 inches to make the final print file.

To get the design with the hex design, i used Makerbot desktop software to slice the STL then I created a customized settings to change the Model properties and change the roof from .80 mm to 0.0. This eliminated the top layer that woudl normally close the print surface. Of course you can skip the customer print and just print it solid if you like