Work, although that's always a bit tricky...I wouldn't recommend that unless you find someone there that you think is just really really awesome.
There always seem to be attractive, intelligent women at upscale health-conscious grocery stores...like Whole Foods.
Local businesses...could be the girl you're buying a cell phone from, etc.
Someone who works at a place you tend to hang out at a decent amount of time...this could be anywhere really.
If you're only 24, the college idea you mentioned could be a good one.
Through friends...they may know someone who they think could be good for you...yada yada yada.
Or join a club that involves socializing like others have said...I prefer the Whole Foods ladies myself.
Hope that gives you a nice start.
I'm sorry to hear about your loss...having a plan for the future suddenly thrown into turmoil can really suck, but you'll get through it. There are plently of women out there, and doubtless there are some who can make you happy.