The .cab file can be found from Chainfire's website (the developer). The latest version is put there first when it is updated.
The website is:
http://www.jongma.org/WMWifiRouter/
The thread that Chainfire checks for issues/other things found with it is on the xda forums.
Here's the link to the thread for WMWifiRouter:
http://forum.xda-developers.com/showthread.php?t=357152
Happy WMWifiing!