To find a replacement clutch pulley for your S3's alternator, you can follow these steps:

　　Verify the Correct Part: Look up the part number for the clutch pulley in your vehicle's repair manual or parts catalog. You can also check the old part itself for any identifying markings or labels.

　　Contact an Audi Parts Specialist: Reach out to an Audi dealership or an authorized parts supplier with the part number and your vehicle's VIN (vehicle identification number). They can verify if the part is compatible with your specific model year and provide you with a quote for the part.

　　Check Online Retailers: Many online retailers offer aftermarket and OEM replacement parts at competitive prices. Check reputable websites such as ECS Tuning, FCP Euro, or Pelican Parts for the clutch pulley part number and compare prices.

　　Consider a Rebuilt/Remanufactured Unit: In some cases, it may be more cost-effective to purchase a rebuilt or remanufactured alternator with a new clutch pulley already installed. This option may also come with a warranty.

　　Remember to always verify the part number and compatibility before making a purchase to ensure that you are getting the correct part for your vehicle. Additionally, it's recommended to purchase from a reputable supplier to ensure quality and reliability.