An ebay power seller under the name cheapchainsawparts (or something similar) stocks a great deal of Stihl parts for your handhelds. His prices are much cheaper than the Stihl dealers. I usually ask him if I don't see something listed and he has always had it in stock.
The best thing is to google whatever you need and don't limit yourself to one place. I am cheap though. If I can save 30 dollars on a part, I will