Hi Preethi,

Thank you for reaching out to Ask Etension with your question.

I believe the grass you are talking about is Elymus repens. It is commonly called Quack Grass or Couch Grass, and it's native to Europe, Asia, the Arctic and Africa. In the United States, it was introduced for forage and erosion control and quickly took over areas. According to the Colorado Noxious Weed Act, Elymus repens is a List C species. https://ag.colorado.gov/conservation/noxious-weeds/species-id#c

It states, "List C are species for which the Commissioner, in consultation with the state noxious weed advisory committee, local governments, and other interested parties, will develop and implement state noxious weed management plans designed to support the efforts of local governing bodies to facilitate more effective integrated weed management on private and public lands. The goal of such plans will not be to stop the continued spread of these species but to provide additional education, research, and biological control resources to jurisdictions that choose to require management of List C species."

Due to this, it will likely be difficult to find seeds for this grass locally. You might try contacting some of the seed suppliers in the following linked document, these companies might have suggestions about where to find seeds for this grass.

 https://cmg.extension.colostate.edu/Gardennotes/566.pdf

You could also try looking abroad for these seeds, a quick google search using the scientific name, Elymus repens did turn up a few vendors in Europe. 

Your best bet will be to find this grass actively growing somewhere next season and digging it up. Once you find a stand of this common plant, you can save the seeds and also propagate it vegetatively to get more plants. I get a patch of this in my backyard every season. The next time I'm digging it up, I will try to remember to find your inquiry and reach out. You are welcome to it. 

I hope this helps!

Dawn