Faithful's legacy files are hosted on their official website or CurseForge. For version 1.8.8, you need the Legacy version (not the new "Faithful 1.8.9+").
If you don't want to use a texture pack, you can achieve the same effect by editing your game files: Minecraft FullBright with NO MODS Tutorial fullbright texture pack 1.8.8
Many players keep a dedicated 1.8.8 installation purely for and UHC Champions because the lighting engine is predictable and Fullbright support is universal. Faithful's legacy files are hosted on their official