Help? How do I buy a license?

I've beaten the Mimic Queen and I'm back in Rabanastre.

The combat is pretty rough. I used almost all of my consumables getting through the ghost-infested tunnels with the battery eater things, and it still took me like 3 hours and several TPKs. I have better spells and equipment but literally every thing I have is like "you need a license to use this".

I have the "Licenses" option in the party menu, but the only option is "Press F to Preview License Board" which just lets me look at all the things I can't spend my hundreds of LP on.

I read the whole in-game tips / manual thing and it said that I could change licenses by "becoming a member of Clan Centurio". I turned in the Angry Tomato hunt and then found that, and the furry at the top of the stairs has an option for "change license boards". But! When I try it! He just says "Kupo-po!? Er, you haven't picked any license boards." Like, MOTHERFLUFFER, I KNOW!!

Sorry for the rant. Who sells the stones / gems / whatever I need to actually unlock the license boards?