I do not think that the postal codes is the problem. Try to find them all in a huge country.
I find these city (or part of a city) as being a depot:
Achères , Avignon Dépôt ,
Béziers , Bordeaux ,
Châtillon-Montrouge , Caen , La Chapelle (Joncherolles) , Chambéry , Chalindrey ,
Dijon Perrigny ,
Lille , Le Landy , Lens , Limoges , Longueau , Lyon Vaise ,
Marseille Blancarde , Montrouge , Metz ,
Noisy le Sec , Nantes , Nevers ,
Paris La Villette , Paris-Sud-Est , Paris St Lazare , Paris Sud Ouest ,
Rennes ,
Strasbourg , St Gervais les Bains , Sotteville ,
Toulouse , Thionville , Tours St Pierre ,
Villeneuve , Vénissieux , Vitry (Les Ardoines)
Source:
http://www.espacetrain.com/