What regions have mercenaries that are worth a type 4 government?

What region or islands have quality mercenaries that merit the construction of a type 4 government? I have captured krete in order to ship out truckloads of archers, and it got me wondering if there are other areas with decent mercenaries. Can i get slingers from the balearic isles or rhodes?
Any input would be appreciated.

I depends on the faction you're playing.
Belearic slingers can only be recruited by Kart-Hadast and the Lusotani, rhodian slingers only by some hellenic powers. You should use the Recruitment Viewer to get exact information. Though both units wouldn't need a type 4 gov.
Cordinau Orca or Thraikioi Rhompairaphoroi need the highest regional MIC's and thus type 4 governments (and are wort it), most other regional units that need this level are faction-specific, again I can only tell you to use the Recruitment Viewer.

there are actually only few regions that profit from a lvl 5 regional barrack. as mentioned above every faction has its own selection of regionals. slingers generally don't need high level MICs you're on the safe side with a lvl 3 gov but most times a lvl 2 would be ok aswell as most regionals only need a lvl 3 MIC.
check the Recruitment viewer to see what your faction can get on level 5. most notable examples are the aforementioned balkan regions and India which is home to indian elephantes
just checked and many factions only have the tracians the scordici and an other unit on the lvl5 regional barrack

1. Tylis (Odrysoi), you can get the Thraikian Rhomp's there!

2. Singidunum (Scorcouw), you can get the Scordisci Elites there!

These are available to every faction I believe.

If you start as Pontos, Ptolemaioi or AS, try Ancyra (Galatia) for Galatian naked's and Taksashila for elephants (Gandhara?) as Ptollies(armoured indians!!!) or AS.

~Fluvius

Aside from those places already mentioned, I believe level 5 barracks are required for some Saka units in India and Baktria. But don't quote me on that, as it's been a while since I played Saka.

afaik the really cool indian and indo hellenic units* are all ll 4 mic only the elephants and armored elephants need lvl 5

*: Taxilan Agema, Sreni Pattya Yoddaha, Agema Hippeon Hellenikon and Agema Hellenikon