I can basically recruit Pheraspidai in every province where I can recruit Hypaspistai (and I think it makes sense), which I can recruit in all Homeland provinces.
Well if You moded it or play different version then 0.81a then everything is possible.
What I and Arkatreides is showing is latest ( 0.81a ) setup.
And You can recruit Pheraspidai in 6 province ( 0.81a ) and Dardanoia is not one of those provinces.