This build of McBrain is bundled with Other (Stockfish) Engines app by Javier. In case you want to install it directly under your favorite GUI without using OEX functionality, you can use THIS binary prepared for arm7 pie devices.
McBrain is a tweaked version maintained by Micheal Byrne. Read more about it HERE.
In case of trouble downloading from your PC, use your mobile device or refer to THIS POST.