Assorted Parts -
There are several Goldwing sites around with a used parts tab but I've found that Ebay is pretty hard to beat for availability and price for anything you'll need. What is odd at times is that most of the pricing is just off the top of someone's head. If you're patient you will often see the part a week later at 10% of the initial price.
Also it seems that the higher pricing follows the ups and downs of the riding season.
Good Luck, Michael