a white carnation if mother was dead, a pink carnation if mother was alive.

that's still in practice around here in places, but it's a bit different: they gave out carnations to each of the moms present, according to the system you've described.

And just how many white carnations did they order?

As previously mentioned, Mothers day is earlier here in UK, in fact it is 3 months before (or 9 months after) Fathers Day .
It was fun getting Mothers Day and Fathers Day cards on different days when our son was working in Oz.

Rod