Nepenthes vieillardii is the easternmost growing Nepenthes species from the island of New Caledonia. It can be a challenging species in cultivation and we recommend reading Francois Mey's blog post. In short, it seems that Nepenthes vieillardii prefers very well drained soils such as the ultramaffic areas where it's found naturally. A mix with a good portion of aggregate including akadama is highly recommended and the plants should dry out a bit between waterings.
The plants for sale are a single clone originally out of Germany, BE-3224.