Nobody can reliably predict how likely a serious pandemic strain of
influenza is to turn up within any given time period.  You may find the
efforts to prevent the current epizootic of highly virulent avian
influenza from crossing the species barrier, described on the WHO web
site, interesting.

As anon says, it's unrealistic to expect predictable numbers for
something that has many variables the affect the results by several
orders of magnitude.

- how virulent is the strain?

- how contagious?

- how early is it identified as a potential pandemic?

- at what time of year is it identified?

- is there a vaccine?  how fast can it be developed? produced in large
amounts? distributed? induce resistance in the vaccinated?  how
effective is it?  No vaccine is 100% effective.

- how willing are governments to take disruptive measures to reduce
spread or prevent the strain from entering their area?  At what stage
of the epidemic?  How willing are people to cooperate with such measures
when they conflict with personal objectives, from convenience to
family obligations to livelihood (or even survival)?

- are most cases in poor countries without the facilities to quarantine
and/or provide good medical care to victims?  do victims have strong
motivation to avoid identification? (the latter was a serious problem
with SARS in China and Taiwan)

- does the pandemic occur at a time when there are a lot of mass
movements of people, e.g. war refugees?

- how healthy are the potential victims?  are they well-nourished?  do
they have a high rate of existing conditions such as malaria, TB,
AIDS?  Note that annual outbreaks of influenza kill about 50,000 people
annually in the US, mostly the elderly and chronically ill.  Western
populations have a high percentage of the elderly, compared to Third
World countries in which the median age is usually about 15 years old.

- what's the morbidity rate?  does it outstrip the ability of people to
care for one another?  when the water supply is hauled several miles on
foot, when fuel is gathered with considerable effort daily, when food
preparation requires a lot of daily labour and most people are too ill
and feverish to even walk to the door, it may not be possible for
people to provide the basic necessities of life for each other.  If too
many people are too sick to work their farms effectively, famine may
follow the pandemic.

In developed countries, hospitals may not be able to handle a greatly
increased load, especially if medical workers are ill or quarantined.
People will also die of other conditions if, for example, surgery has
to be postponed.

I hope you can see that the numbers you want can only be obtained after
the pandemic is in full swing, if then.  Epidemiologists can model, but
with all these factors that are so difficult to quantify, even an absolute
worst imaginable scenario isn't so easy to develop, much less one that
has any real predictive value.

If you study the material on the SARS epidemic, you'll see how single
acts by a single person can have far-reaching consequences.  A doctor
from Kwangtung went to Hong Kong to attend a relative's wedding.  He
infected a number of people in the elevator lobby of the floor of the
hotel he was staying at, perhaps with a single sneeze or cough, and
these people carried the virus to several countries of southeast Asia
and started epidemics there.  One hotel guest was an elderly woman who
returned home to Toronto.  When a 78-year-old diabetic woman with
chronic heart disease develops the symptoms of flu and pneumonia in
February, very few doctors will consider the possibility that she has
an unknown and dangerous epidemic disease.  She died two weeks before
SARS was recognized as a new disease, and she was the index case for
the epidemic in Toronto.  Most victims in Toronto, and almost all the
fatalities, were among elderly people sick enough to be hospitalized
for other conditions -- strict and very expensive quarantine measures
kept it out of the general population.  The same was true in Singapore
and to a lesser extent, Hong Kong.

The point is that a sneeze by one person in one elevator lobby caused a
world-wide epidemic, though very fortunately a very well contained one
that killed less than a thousand people.  Had it gotten into the
general population of areas like India or Africa, the death toll might
have been in the millions or tens of millions.  You can model this
scenario, but you can't forecast the future from it.

Note that SARS is a great deal less contagious than influenza.