There should be no need:
$ brew search android-sdk
If you meant "android-sdk" specifically:
It was migrated from homebrew/core to caskroom/cask.
You can access it again by running:
brew tap caskroom/cask
Packages get migrated from brew to cask when it's deemed that a binary release is the canonical release rather than a built from source release. If you really do need a previous version of the formula installed, it's possible to create a versioned formula to track the previous version. I'm not sure that this is supported by homebrew cask though, so this might be a more difficult question than you're asking.