Do you have a 4-H leader that knows anything about chickens? That would be the best place to start.
Sebrights are cute little things, I think they'd make great show birds. They're not known for being the calmest, though, or the easiest to handle, so you might take that into consideration for something like showmanship.
This time of year, hatcheries are gearing down for the winter and sometimes selection is limited. You can look at My Pet Chicken, they have a minimum order of 3 chicks, but I'm not sure if that applies to bantams or not. If there's anyone else in your group looking for birds, maybe you can split an order? I've done that some and it's worked out well, you just have to be sure you're ordering breeds you can easily tell apart, or have the hatchery mark them!