How many of us are out there?

We are preparing to conduct a Perma-Workshop next year, "Introduction to Permaculture". As the Title suggests, it's meant to attract beginners who have heard about Permaculture, but don't know much about it. I want to hold a talk at the end, pointing out where we are right now and what could be possible strategies for the future. For this, i'd like to compare different green movements which developed over the last 35 years in terms of strategies, numbers, influence an so on.
Are there any hard numbers about how many permies are out there? A friend of mine reported from the permaculture conference in london this year that Geoff Lawton mentioned the number of 1 million people having completed a pdc since end of the seventies.
Is there any source for this i could quote? Is there a monitoring of the numbers, do we know, how fast (or slow) the movement is growing?

I'm grateful for every hint...