Dodge Viper Central
Where to Buy a Used Viper:

Dodge Certified Preowned - Buy from a dealership to build a relationship with the sales and service staff.  Whenever I dropped off my Viper for service, the sales guy always took care of me for my rental car.  I got to know the service manager who sold me a Viper warranty at cost.

Viper Club of America - Buy directly from Viper owners at this board.

eBay Motors - A bit riskier, but hey you can probably find a good deal or two here. - Find a mix of private party and dealerships selling cars here.