Bite the bullet and download the official Steam version. Use the "Low Storage Mode" and uncheck high-res textures. Leave your computer on overnight to download the 25 GB.
Valve itself uses BSPzip to compress map files, which can reduce the maps folder size by up to 38% . The Risks of Third-Party Downloads team fortress 2 highly compressed
: Use the CompactGUI tool to apply transparent compression to the TF2 folder. This can shrink games by 30% to 50% with almost zero impact on performance. Bite the bullet and download the official Steam version
(Legit method)