I grew some agi's fron seed just by sowing in light compost on a window sill in early spring. They took a long time to germinate, so you have to be patient, and they take several years before you have a flowering plant.
That's if the frost doesn't get them first.....

Sow in early Spring, they need a bit of cold to help germination. Then follow the instructions on growing Alliums from seed.
http://www.growsonyou.com/question/show/2941-growing-allum-from-seed