The only reason I can think of not buy those would be to buy these.
There's a set going on ebay.com (not .au) that ends in 20mins currently only US$315
http://cgi.ebay.com/ebaymotors/Keihin-35mm-FCR-Carbs-Ninja-CBR-YZF-_W0QQcmdZViewItemQQhashZitem414fccc57eQQitemZ280511694206QQptZMotorcyclesQ5fPartsQ5fAccessories#ht_500wt_956
They're a bastard to tune apparently but once you do they are supposed to be better than just about anything.
'tiK.[hr]
Actually scrap that. They're only 35mm and I reckon you might want something larger for a 900.
'tiK.

There's a set going on ebay.com (not .au) that ends in 20mins currently only US$315
http://cgi.ebay.com/ebaymotors/Keihin-35mm-FCR-Carbs-Ninja-CBR-YZF-_W0QQcmdZViewItemQQhashZitem414fccc57eQQitemZ280511694206QQptZMotorcyclesQ5fPartsQ5fAccessories#ht_500wt_956
They're a bastard to tune apparently but once you do they are supposed to be better than just about anything.
'tiK.[hr]
Actually scrap that. They're only 35mm and I reckon you might want something larger for a 900.
'tiK.