You order from the official rakuten shop of Sanwa, it's good. they provide exclusive color.
althought the official shop not ship overseas, but you can try http://www.tenso.com/chs/ ?
http://www.rakuten.co.jp/rs-2006/
this shop provide sanwa silent joystick (no silent buttons avaiable) and other brands, willing to ship oversea , you can ask them to estimitate the shipping before confirm the order.
Last time I ordered 25 buttons and the shipping cost is $1380 yen