You can get much of the needed information by using tools from the Internal Revenue Service (IRS). The run-up to (and the few days after) Presidents Day are the busiest time of the year for the IRS. It can take over an hour to get through to the IRS by calling if you get through at all. The online tools are faster and more convenient.
Since the shutdown started in December, the agency has been operating under a plan that had fewer than 10,000 employees working during the shutdown, mostly to keep computers running and investigate crimes.