Ciao Francesco,
accoridng to this link
Paphiopedilum papuanum and to Koopowitz' book this is a very rare species... (and very difficult to grow or even keep alive)... Olaf Gruss (different forum) confirmed how rare the species is and taht it is known in only very few collections... none of the references given above has made a reference to f. album... if indeed there is a f. album of this species, and it is for sale, I would expect an astronomic price!
given the info above, I would doubt whether the plant offered is even Paph. papuanum... is it a well known (and serious) vendor?
Post note: I found also that apparently, most of the Paph papuanum on sale are actually Paph violascens or Paph. bougainvilleanum (Paph. bougainvilleanum f album is known!)