I was trying to find an exploded parts diagram etc. to see the setup but if the mechanism was external, it would be fairly visible and you wouldn't have to hunt for it.
Bearing in mind the family tree, I suspect it's an internal system like the Stilo has.. so it presumably has a cubby hole holding the adjuster rod, underneath the console.
Alternatively, in the older Fiats/Alfa's I've had, the handbrake lever shroud has been able to pop off and the handbrake cable adjuster threaded rod was accessed underneath the lever (albeit you needed a very deep socket or an open-ended spanner to rotate the nut. Fiat may reverted to this style, if a console is fitted.
Ralf S.