http://www.edsonmarine.com/marinestore/index.php?main_page=index&cPath=85 (Pedestal Accessories)
http://www.edsonmarine.com/marinestore/index.php?main_page=index&cPath=87_99 (Instrument Mounting Accessories)
Generally, the common principle is that you run the wiriing through the pedestal or binnacle guard tubing if you have one. There are others that make quality instrument pods. They are generally sized to fit on standard Edson SS installations. ( NavPod, Scanpod, and Seaview for example) Go to Defender.com or look at their 2010 catalog on pages 277-280 ish. You can pick-up Edson parts from a number of "retail" distributors other than directly from the factory (like Defender or West Marine) too.
In this case, I wouldn't reinvent the wheel (pun intended).