Good job finding the problem.
That overload should automatically reset one's it's been tripped.
It will trip if the motor got to hot or if the motor is drawing to many amps.
You can't purchase the motor overload as a separate part. Even if you could chances are there is something not right with the motor that caused it to fail anyway.
A new motor will come with a new overload installed on the motor. Your model dryer uses motor part # W1041099
How old is the dryer?