Financni odbor
When you first register your zivnostensky List. The zivnostensky office "should" register you with the relevant financial offices.
One solution is to register yourself. It can save a lot of trouble at a later date. And you know that you are registered.
If you use a company to make your papers for you, make sure that they register you with the Financni odbor.
If you register yourself, you need to register with the Financni odbor/Urad in the area where you registered your company.