I have head someone else mention the fief less clans but you still need to (a) find them, (b) win the minigame. organically this hasn't happened and if this is the only way to achieve more clans to your kingdom i'd argue the mechanic is broken and still needs fixing imo
I did try a cheese myself - i downloaded a mod that makes free clans apply to your kingdom in the same bay as M&B Warband (excellent game!) but sadly it makes my game crash. I may honestly see if there is a way to command line (straight up cheat) assign a few clans to my kingdom just to finish the run...
Don't get me wrong, I totally agree. Once again, during hundreds of hours of playtime, I've only managed to recruit a clan trough normal means, once! And that's not all, when I originally posted this issue on reddit back when, any clan once recruited (and positive relationship mean nothing back then) any clan, once recruited, would bail within a day, regardless of the sum you paid him. But here we are, it's still early access. I'd say TW should address this ASAP, but theyv've come a long way I'd say. Give it time and give feedback, it seems the devs (or at least the community manager) is quite active on these forums.
In the meantime, Use my cheesy workaround I've described here. It works, but takes time and effort.
The way it used to work in WB was a bit too extreme (fiefless clans would flood my city), here in Bannerlord, it's nigh impossible, but I'm sure the devs will fix it eventually.