Possibly related- 'Two great white oxen' appear in the legend, "The Sin of the Prince Bishop," and on a Catholic holy card. Three hits in Google on the phrase; Christmas in legend and story is the heading of one that may help with ideas, but no song found..

From the front, from the back (rear), is from a bawdy soldiers' song. Someone may remember it or have words.

From Vichy comes the call- ?

I suggest that you get a copy of the play in French; it may help with the titles and in tracing the songs- translations are often of little help. Abebooks has three copies on offer (Dreyfus, L'Atelier, Zone Libre, all in one). There is a recent French paperback.