Habemus Papam: who organises the white cassocks?

Just a thought ... the new Pope appears for the first time on the balcony only about an hour after being elected wearing for the first time the white papal cassock ... so how did they get him fitted out so quickly? Do they have a stock of them in all sizes? Do all the cardinal-electors have to give the Vatican their measurements in advance of the conclave so they can have enough ready so that there's one that will fit whoever it is that is elected? Not of huge importance ... just the kind of thing that inquiring minds want to know!