You should buy a new one. On the existing one you should find a number such as 313-5190, these numbers are a guess, the point being 3 digits dash 4 digits. Google that part number and you should have a wide range of sites to choose from. If a number is not present try the pump model number if it is present or post a comment to this answer and I'll try and track one down for you. Another alternative will be a local electric motor/pump repair shop or a pool/spa store.

John