We use both spellings. On the website I can order that really delivers here, they only sell 3 boxes of 6 (so 18) at once. Never seen 18 in 1 package. A couple of years ago we ordered 10 boxes of 6 with a group to save shipping costs. But I still use my first order from years ago, I am a person that normally always can clear ears, even with cold or fever. So I don't worry directly that we cannot buy it here. Most of the Belgium pharmacies stopped ( I think because of law) with shipping to the Netherlands.
But as you see, different countries, different rules.