I really like Cottage Rose n' Blossoms.
She has some very high quality Sebastopols, but you need to get a reservation in!
I'm not sure about other places, but Sebastopols are just about done and over with laying, you'll have to get a juvenile.
Balbinka's egg (my Sebastopol) came from Freestep Farm. I'd highly recommend her (Carla, the breeder) as well. She is very honest, genuine, and cares about the results of your hatch. Her stock are from Holderread, and she keeps her flock to a relatively low number of geese to offer them the best care.