Procurement for business/government/military (including and especially NASA), is very different than what you would see on a shelf at your local drug store.
The drug store can't buy a single box of tampons. They have to get an entire case of boxes of tampons. If each box is say, 20 tampons, and there's more than 5 of those per case, then they're buying at least 100 tampons so they can get a single box of them.
There's a lot of alternatives they could have looked into, like neighboring government institutions which may already stock them, asking them to supply a smaller quantity than they would have needed to order, or ordering outside of their typical channels and sending the intern down the road to buy a box from the nearest pharmacy... Those things wouldn't really get accounted for in their budgeting though... So they would prefer to order through their normal distribution.
It's a funny comment to make to Ride, "is 100 enough?" And I'm sure everyone had a good chuckle.
Regardless they probably didn't see another good option for ordering other than to just buy a case of them and figure out the rest later.