Where can I get a TPM for Asus sabertooth 990fx r2. 0?

i have windows 8.1 pro and want to use bitlocker. i want to get a TPM for my MB. dos anyone know of a good TPM?

http://www.amazon.com/Asus-Accessory-TPM-FW3-19-BitLocker/dp/B0085E4WQQ