Mark,
There are several companies that are in that market. Most of them focus on HO scale since its the most popular scale at this time. The two big boys are Woodland Scenic as you found out, and Scenic Express (
http://www.scenicexpress.com/).
I personally lean toward Scenic Express ground covers as they seem more natural to my eye. But Woodland Scenic is so easy to get, I use it also.
Your biggest problem (I don't mean that in a bad way) is your modelling Z scale. Which means you will need really fine material to make it all look like its proportioned correctly. So in the case of ballast, you should look at Highball Ballast(
http://www.modeltrainstuff.com/Highball-Products-s/1255.htm), it is more expensive than Woodland Scenic, but it is more proportional to smaller scales.
When it comes to ground covers, and other scenery aspects, I think you will find other niche products, but will end up going back to those two manufacturers over and over again for general purpose supplies.
John
