There's a Cash Box Request form you can download from the File Exchange on this site. We would write the check to Cash, and then verify the $ in the cash box at the start of the event. (Use a Deposit Form to log the money in the cash box at the end of the event)
I agree with DLF - this is a different situation. You typically don't want to write a check for "cash" for general, undocumented spending.
But the cash box is a specific disbursement. Usually you'd have a simple form detailing how much is in the cash box, maybe down to the denominations. The treasurer would initial that this amount of money was being provided The person working the box verifies the amount and initials the form in acceptance.
Why can you not write a check for cash and have it verified as the cash box money? That's sort of odd. I guess you could have someone supply the cash and then reimburse them after the event. Not sure why you have that restriction on yourselves.
I'm a new treasurer, and we have events that need cash boxes for change. We are not supposed to write out checks to cash to get the change. So what do we do? Who should the check be written out to so K can get the cash for the cash box?