I note that patch.winmxconex.com is online now. Cannot get patch.winmx.com, but it is the first site that you want!
Even though there is not a patched 3.31 available, you could probably get the oledlg.dll and copy it into the same folder with your winmx.exe, usually under Program Files/WinMX. We were being encouraged to upgrade to WinMX 3.53/3.54 back at the time EaglE's new Community Patch was released. You would gain some advantages. If you want to enter a room that is hosted on Zenar Chat Server, you will find you need to update your WinMX. 3.31 is slightly older protocol. I believe however that oledlg.dll would work for you.