When I scrapped my Xantia, I removed the automatic wiping sensor and wiring so that I could possibly fit it to a BX - so I removed it as a stand alone kit if you like.
I won't fit it to my BX now so it is up for grabs.
The wiring will need to be spliced in to the relevant wires in your Xantia so it's not a straight forward plug and play but for those who are electrically minded I don't think it would be too difficult.
You'll need part # 6405E1 which are the metal brackets used to secure the sensor to the windscreen. These are £12 from Citroen.

£20
located at CF38 or can post at cost