Well, I guess it depends on what you mean by late summer grass - and where that is. Could be anything from a rich, deep green color to a patch of mostly dirt with some 'blonde' left overs of blades of grass. Here in California it's going to be long swathes of blonde grass, mostly. Or rather black if after a good (or very bad) fire. You've checked with Noch and Scene Masters, JTT?
I'm not able to recall the name, but there was a company that sold matts at 12" x 12" of California's golden grass. I think the company is in Utah or Colorado (USA) now. I found the product very useful - they also have a spring green and a summer green. And dang if I can remember the name - ought to be asleep in bed.
edit: Grand Central Gems! See what a night and a bit of sleep can do for the brain. That is the company with the spring, summer, and California blond grass. All useful within my collection. Not sure if it is still available but double check there web site.