Rockywwods used to have it but i think they're out of stock now. I would try emailing them to check future availability.
You can try ebay, often i see people selling multicam cordura and nyco fabric by the yard (expensive shipping though).
Have you thought about butchering an old-and-cheap used uniform shirt? the back area has plenty of fabric
Ya Rockywoods was the first place where I look at but it was almost the only one which I knew selling mc nyco. I have also considered ebay, but since I would like to get what I pay for I don't know is those mc nycos good quality or not. I am living in Finland and all the sellers are located in states so there is no possibility for me to return if the quality is not what I am looking for. And what no I have not thought to butcher any of my shirts, but since you said that I may have some Propper multicam jacket hanging on somewhere. I have also a little hurry with this so if I can find that jacket it will be butchered since its fastest way to do this.