Yamaha's extended warranty (YES = Yamaha Extended Service plan) can be purchased at any Yamaha dealer.
Several forum members have purchased the YES plan from an ebay seller for a large discount. It may be wise to do a search on Ebay or Amazon or always ask on the forums for the latest info and lowest prices.
NOTE: Yamaha ran a promotion in 2006 which provided owners with a 48 month YES plan for free when they purchased their 'liner. Not ALL 2006 'liners were sold under this promotion.