SPRINGFIELD — Fighting what they have called the “harshest ballot-access laws in the country,” several third-party candidates filed to run for state offices this week.Claire Ball and Kent McMillen, Libertarian candidates for state comptroller and the U.S. Senate, respectively, were required to gather thousands more signatures than either the Democratic or Republican candidates in their races.But on Monday they said their campaign operation filed more than 53,000 signatures with the State Board of …