I just returned home from the Ukraine and brought in a bag of "Buckwheat".  I don't think you will have a problem.  Just fill out the "customs" card you receive on the plane.  They are more obsessed about plants, fruits, seeds, and vegetables that may bring in unwanted insects and such than regular food.  They are also more likely to be observant of larger monetary sums of "duty free" items, which I think there is a limit.  The immigration officer will probably ask what your starter is????? because it's an unusual food item, but with a short explanation, he will most likely be accomodating.

There are pretty strict regulations regarding carrying on any type of liquid, lotion etc. Even sealed tubes have to be thrown away. My guess is that you won't be able to carry it on. Good luck.

Curious to hear.

For future reference, I know there are some threads here that talk about drying a smear of your starter for a few days on a coffee filter and then just carrying it dry to the new location.Soak it in a little warm water and innoculate some flour and water with it, once you get to your new location and start building an instant starter. (The coffee filter would withstand a soak in a little warm water better than a paper towel or napkin.)Ingenious!