This Homebrew tap allows you to install Qt4 (and various packages that depend on it) on macOS Sierra and newer. You can install it like this:
brew tap cartr/qt4
brew tap-pin cartr/qt4
brew install qt@4
Feel free to submit an issue or pull request if you run into any problems or have any suggestions for improvements to the packages.
Please note: Qt4 is unsupported by its creators, so there are likely security/usability problems with it that will never be resolved. If you can, please consider migrating your projects to Qt5.