Dunno either but you could do as I did and fill the hole with a match stick etc and reuse the nail. My one on embryon has not come out in two years.

Thanks Rob, I'll be doing that as well but a couple of the nail heads are really crooked and just don't sit flat so I'd love to find some new ones. Try googling twisted nails and you end up with lots of pics of colourful twisty stick on finger nails.