You can find some of the hairgrasses for sale in seed form sold as spike rush or rush. Rare, but it exists..
I've seen those seeds. They are like brown seed thingy where a green grass sprouts. It's very abundant in our country. It was usually seen in the emersed form of hairgrass. It takes a whileee when you plant those seeds. Mine takes a month in a 2.5wpg to grow from seed to full fledged hairgrass. But it's very interesting to see it grow. :P