Not sure about other European countries but over here membership to the national sailing organisation is mandatory if you want to compete in "official" races (races of all the ISAF registered classes).
Some events have an exemption from this rule (actually only Texel really), this is solved by having the option to enter as Gold or Silver fleet.

Membership to the national organisation runs through the yacht/sailing clubs, I think something like $10 is transferred from every membership fee (total membership fees are usually between $50-$150/y depending which club you want to a member of obviously).

What does our national organisation do for catsailors?
Probably about as little as yours does by the sound of it, although they have ordered a pair of N17s so I guess that is money well spend for the Olympic hopefuls.