I just got a 4" pot, stuffed full, at a local garden center for a few dollars. It's grown emerse in the "Steppables" line of garden plants here in the PNW and probably around the country. The Eleocharis radicans (on the label) is the same as E. acicularis.
I'm flushing out fertilizers and raising water level on it to adapt for the aquarium. Probably just washing it well would be good enough, but I don't have the tank set up yet anyway. It's cheaper than even just the shipping, this way, and you get a lot more than the rockwool plugs from a LFS (which is almost always emerse grown anyway).
Correction... it wasn't a local nursery, just remembered it was either Home Depot or Fred Meyer (Kroeger).
I went to 2 home depots and asked the people in the gardening/plants area if they had any emersed plants or plants in water, and they just had blank dumb stares on their face. Did you have any luck Jeff? What plants/area did you find the hairgrass near?