You can get to the Foyer Sainte Marie :
By tube : station Vavin (line 4)
station Notre-Dame des Champs (line 12)
station Raspail (line 6)
By suburban train (RER) : station Port-Royal (line B)
By bus : 38, 58, 68, 82, 91
Click here to visualize the interactive map of the public transports.
Have a look at the stations situated near the Foyer by clicking on the image below