First of all, you need MGE SVN rev118.
The shader is available http://www.speedyshare.com/586255660.html. (v0.02a)
Edit:
If you have changed your Field of View (FOV) via MW FPS Enhancer or any other tool, you will need to open the shader fx file with a text editor and find the line '#define fov 75'. Change the 75 to the exact FOV setting you use. Otherwise the sun movement on the screen will not fit to the rest of the screen.
Screens:
http://img228.imageshack.us/img228/4300/85156292.jpg http://img196.imageshack.us/img196/3271/27026476.jpg http://img228.imageshack.us/img228/1847/70229522.jpg http://img205.imageshack.us/img205/2743/25510631.jpg http://img205.imageshack.us/img205/782/51944443.jpg http://img215.imageshack.us/img215/9639/65128684.jpg
Personally, I think this shader makes MW's sunglare obsolete, so I have included a completely transparent sunglare texture in the zip file to get rid of it. It will still work if you keep the sunglare, though it may look too bright and kinda strange when MW's sunglare keeps popping in.
This shader should be placed before bloom in the active shader list, to make bloom work on the sun rays. I have included some tweakable values at the top of the shader file, so you can adjust the shader parameters to your likings. I've also tried to describe what each parameter does. I have found that the strength of the bloom shader you use has a great effect on sunray brightness, so you may need to adjust the 'raystrength' variable to prevent overblooming.
Edit:
Updated to v0.02a