Events button is not alaways available in Source since it is actually design view functionality and is only available when designer is synchronized with source. Instead of switching views you can work in Split (just make design view small) and click 'synchronize views' yellow bar - this should make event button reappear. 

This is by design, see more info here http://blogs.msdn.com/b/mikhailarkhipov/archive/2007/01/23/how-does-split-view-work-in-vs-orcas.aspx