A reputable community archive containing various versions, including 1.31.1. RepackGames (Method 1 in Reddit threads) Listed in communities like
Keep your original CD keys safe. Support map makers. And never let Blizzard’s auto-updater touch your installation folder again.
Patch 1.31 is the standard for (competitive ladder) and Eurobattle.net .
Note: Only use if you own a legitimate CD key and cannot use Battle.net.