I have used both of the following people to buy Shimano reel parts. Word of caution.....be patient, especially if they don't have it in stock and have to order it.
http://www.mikesreelrepair.com/
Hey.....Mike's is in Canada but their prices are in US dollars. Their site can be tough to navigate, so it might be best just to give them a call.
http://www.buckosparts.com/
Not much of a website here either so best to call them as well.
Best to get your hands on a schematic of the reel so you are looking at what they are looking at. If you don't have one, try here....
http://www.mikesreelrepair.com/schem...ls.php?album=8
Don