iFixit carries both the black and white versions of the iPhone 4 front panel. From the product description:
"This part contains all the necessary components to replace the front display assembly. It is a complete part with the LCD and the glass fused together. It includes the speaker grill installed.
This is an Apple OEM part, not a copy or imitation."
Hope that helps!
Includes the LCD and the front panel glass. — 50+ available at 94.95 each.
I haven't found a place where you can buy the front panels yet. iFixit will have them in stock shortly, but we at testing them first for quality assurance.
I did find a service which claims that they allow you to ship them your iPhone, have it fixed, and returned within 24 hours of them receiving it. http://cgi.ebay.com/iPhone-4-Cracked-Gla...
I can't vouch for their quality or credibility, but that's all I've found.