Chance to find HMAC key/salt when having knowledge of the hashed data?
Assuming you mean a normal HMAC with a strong unknown key, no amount of MAC values for known, or even chosen messages would help you find the key. That would mean a failure of HMAC's forgery resistance, which is expected of MAC algorithms.

(It would be a very bad case of forgery attack, since it would allow forging MACs for any messages. Even much lesser attacks, like being able to forge a single valid MAC for another message, would be considered significant breaks.)