@Jagganath
If you're looking for a quick way to play the scenario, the board game Zombies!!! actually has a very good scale. I just opened the box yesterday and thought "Wait a sec...are the 20mm?". They aren't on the same level sculptwise, but you can get whole bags of them for cheap.
Yes, the Zombies!!! are 1/72-ish and work great with 20mm Elhiem and Dark Future minis, and other 1/72s. I have hundreds of them painted up; sadly the photos are lost on some image hosting service that dramatically changed its terms, grr.
In general Elhiem's figures are great, I have many of them in my survivors but I have not ordered any of their zombies since I am pretty wealthy in those plastic figures.
I also used 15mm Rebel Minis for teenage zombies and armed survivors.
n.b. the Hannah Montana Mall Madness game works great in this scale!