Amazon sells these. Look for a FIDO compatible key. FIDO is the security standard that Google uses for device based 2-factor authentication. You can buy keys from as little as $6, and up to $50 with NFC built in. NFC is a wireless standard you can use with your cell phone to transmit a code to your phone. NFC allows you to use your key on your mobile phone, thus if you just want to use your key to access Google on your computer you can just buy a $6 key.