I haven't bought any grasses. All but one have been grown from seed, most using winter sowing techniques. The one exception is a division of Panicum virgatum 'Shenandoah' which I traded for.

Here's my full list of successfully winter sown grasses:

Anthoxanthum odoratum.. Sweet Vernal Grass
Briza maxima.. Annual Quaking Grass
Briza media.. Quaking Grass
Carex grayi.. Gray's Sedge
Carex muskingumensis.. Palm Sedge
Chasmanthium latifolium.. Northern Sea Oats
Cortaderia selloana.. Pampas Grass
Deschampsia cespitosa.. Tufted Hairgrass
Eragrostis spectabilis.. Purple Love Grass
Festuca gigantea.. Giant Fescue
Festuca glauca.. Blue Fescue
Festuca mairei.. Maire's Fescue
Festuca scoparia.. syn. Festuca gautieri Bearskin Fescue
Hystrix patula.. Bottlebrush Grass
Lagurus ovatus.. Bunny Tails - Annual
Luzula nivea.. Snowy Woodrush
Luzula sylvatica.. Greater Woodrush
Miscanthus sinensis.. 'New Hybrids' Maiden Grass, Eulalia Grass..
Nassella tenuissima.. Mexican Feather Grass
Panicum virgatum.. Switch Grass
Pennisetum alopecuroides.. Fountain Grass
Pennisetum alopecuroides.. 'Moudry' Black Seeded Fountain Grass
Sesleria caerulea.. Blue Moor Grass
Setaria faberi.. Giant Foxtail - Annual
Stipa capillata.. Feather Grass
Tridens flavus.. Purple Top

Note that there are few 'named' cultivars and no variegated or uniquely colored varieties on the list. This is because, in general, one can only grow species, and not cultivars from seed.