We come to work all the time and the time sheets that we have to hand fill out are not available, HR hasn't sent them out. Is there a law that says these time sheets must be made available on the day you work? We are regularly called in on our day off and there is no time sheet to write down your hours. Or the time sheets are taken up early because of a weekend or holiday, so you can't write down your time? You have to wait until the next week when HR is back to track them down and add your time. Our fear is that sometime we are going to forget a day and not get paid for it.
Seriously, take an empty sheet of paper, write “Timesheet” and your name at the top, and fill in your hours.
If that isn’t accepted by HR then ask here again.
And if they are not paying for time that you worked when they are messing around with time sheets, call them and demand that it is sorted out immediately. Not paying you for your work is unacceptable and illegal in most places.