I have found them from several sources but live in the USA.
These tips may or may not work as well in the UK:
1)
ebay (ebay France is very good for French bikes and parts);
2) local cycling club or regional bike swaps that attract buyers and sellers of classic /vintage bikes;
3) smaller and older bike shops, especially former Peugeot dealers;
4) Here in the states we have Craigslist, a localized nonprofit-based digital "classified ad pages."
You may have something similar online in the UK.
Search for "Atom," "Maillard," and "Spidel" skewers, depending on the quality level and vintage of your Peugeot.
You should be able to find some soon.