I think I'm confused

I'm sorry if this is redundant and is answered elsewhere (in which case I'd appreciate a referral) but I'm having some problems with the MIC's, namely that I don't seem to be able to build them. I'm playing the Romani and the factional MIC's don't appear available anywhere outside the first five provinces. Is this by design? Am I missing something?

Yes, it`s a feature. Factional MIC`s with the romans are only buildable/upgradeable in the core 5 provinces of the republic. With other reforms, namely polybian, marian or augustan, your recruitment options will progresively enlarge.

But for now, the only places you can recruit "Roman" units, are in central italy.

This is by design and intended to mirror the way the Romani legions worked in the Camillan Era. Once you undergo the Polybian reforms you should be able to recruit troops from about 10 regions, and upon reaching the Marian and Augustan reforms you'll generally be able to recruit legionaries in any Type I or Type II province.

Currently you can recuit Camilian in five and Polybian in six towns.

Correct. There were some bugs in 0.80 with building placement.