If they are as hard to find as the Marchal TP21SP lights then it's probably cheaper to buy a scrap Viva for £50 and join the club
On a serious note the non-concave ones are Renault 11/12 I think and now seem to fetch a huge premium. There is a guy on Ebay based out of Lebanon (the sandy one not the one in the USA) who I think now wants $350+shipping per set.