Renderosity has this package:

http://www.renderosity.com/mod/bcs/tears-for-v4/90723/

...but alas, it's V4 only.  I want to make my M4 men cry, too :-)

I couldn't find anything (here or elsewhere).  Jepe's has a package over at That Other Place but it's pretty pricey ($15 for each character).

Is there any other option for adding tears?  It's easy to give characters a crying expression but the actual tears running down their face...?

Or do people usually do that in post?