To unlock the Club Clothing options you have to have the club your sim is in to gain points, and after a certain number of points, you can purchase the clothing items. Here is more information about this. https://www.carls-sims-4-guide.com/expansionpacks/gettogether/clubs/perks.php
Now if you don't want to bother with it, someone has created a mod where it will unlock CAS items, and you can pick the ones you want.
https://fogity.wordpress.com/mods/unlocked-cas-parts/
Just want to let you know that with this mod, you can remove the mod, and those items you place on your sim(s) will stay on them since they are EA items.