As C. balearicum can't be that common in the Cevennes, I'd suggest that anyone who does know of likely sites emails Jo privately. Giving locations openly here on the forum would be too helpful to the dreaded plant-diggers!
Hope you do find some, Jo - and hope to see some photos here.
Yesterday Helena and I went further down the Mani, to the site of some very late-flowering C. hederifolium (the sort that has recently been called crassifolium) - will post a photo when I get back to UK in Feb.