ebay has a number of white speakers that would work. Some old Minimus 7s from Radio Shack. Not a bad little speaker. There are a number of Boston Acoustics speakers that would be appropriate. The Mirage Omnisats may be your best choice for surrounds due to their wide soundstage. There is also a pair of B&W Rock Solid speakers, which may be the best deal of the bunch.
Anyway, just search for "white speakers" on ebay and you will see many options. Just avoid the Bose, Pyle, and Klipsch options and you should be fine.