Is there any blockchains that has implemented a 2fa type of security measure? Currently someone can steal your btc private key and send all your funds away. But has there been a 2fa built into a blockchain that prevents something like this? 

Say if you wanted to send something out from a btc address, it will require a 2fa generated token text to be provided in order send out.

I'm not talking about exchanges, but just the blockchain itself.
text to be provided in order send out.


Who would be sending this SMS, who would be generating the secret?

The Bitcoin blockchain does support multi factor authentication by way of OP_CHECKMULTISIG, where you can have multiple keys simultaneously control a single output. This is auditable (you can tell what keys signed) and requires no third party trust. 


  Currently someone can steal your btc private key and send all your funds away.


Quite literally, the reason for wanting to protect the private key from being stolen in the first place.