I've just developed a block cipher symmetric-key algorithm and I am using it in some of my products. I want to put it to real test.
How would one go about entering their encryption algorithm into an international encrytption contest?
Yes but they are normally the other way around.
Well respected experts in crypto are invited to submit their algorithms and everyone else in the world is invited to break them. The one that does best ends up as the next standard. These algorithms have already stood up to the mathematical tests of their own inventors, their students and fellow researches as well as the experts at various inteligence agencies.
Sorry but nobody is going to put time/effort/resources into trying to break an algorithm by an amateur with no reputation, publications or standing in the field.
Use it to control access to non-trivial amounts of money, in public. Wait some time. If you still have your money, it's strong enough.