Apple has released the second developer beta for iOS 8.3. This comes along with the second beta release of Xcode 6.3. Both are available for download in Apple's iOS Developer Center.
The iOS 8.3 beta is currently only available in the Developer Center, and is not yet appearing for download directly on iOS devices running the first beta version. The first beta of iOS 8.3 was released in early February.
Source: Apple Developer Center