Where to get Win 7 RC2 Build 7231?

There is no such thing as RC2. All builds past 7100 are internal only, and the only way to get one is from non official sources. Such non official builds are not support nor recommended by Microsoft. You should use the build 7100 only, and wait for the final release. Builds past 7100, once non official, are not to be discussed in this forums.