I don't know if you can buy that online...
But the skirt looks like you can pull off a pleated skirt. Which are very easy to do.
The shirt just gets a white collared shirt cut the sleeves off, and hem it. Black tie is easy enough to get. and there might be some tutorials for the arm warmers floating around on Cosplay.com...
Just my input on this.
Planned New Cosplay for near future (in order of listed):
Monica (Dark Cloud 2) 5% done
Eclair (Dog Days) 0% done
Nai (Karneval) 0% done