You could always remove the hidden resource Rome from them and be able to train them everywhere.

All you have to do is go to export_descr_buildings in your RTW Data folder and change the line from this:

Code:
 recruit "roman legionary first cohort i"  0  requires factions { roman, }  and hidden_resource rome and marian_reforms
to this:

Code:
 recruit "roman legionary first cohort i"  0  requires factions { roman, }  and marian_reforms