There is no way to say with certainty if it was used by a railroad, or if it was, what it was used on. One thing though is the chain attachment was rarely ever used by homeowners. The reason being the chain option added several cents to each padlock - a fair amount of money in those days. The chain was specified for industrial applications where the lock might have had the chance to “grow legs and walk away” once unlocked from the hasp it secured. So in the myriad of things railroads needed to keep locked, it could have been used by one.
Finding a working key would be an excercise in futility, one could always be made by a skilled locksmith, however the cost would sadly exceed the cost of the padlock.
It is neat though, thanks for sharing!