Where did you purchase your KM from? Tell your vendor politely that your KM didn't come with a hose grommet.
In the mean time, you can use a piece of a wet paper towel and wrap it around the end of the hose so its airtight on the stem.
I believe hookah-shisha has some: http://www.hookah-shisha.com/store/p...idproduct=1063
But ask them in advance if their grommets are compatible with your hookah.