Just say "Hey, I am heading out but let me have your digits so I can call you sometime."
Presto. Number.
Then wait until you feel good about it and give her a call and say "Hey, this saturday I was thinking that we could go do X. I'm thinking I'll pick you up at 7." If she is interested she will say ok or suggest an alternative.
Presto. Date.
Not that hard buddy, their aren't any magic tricks. You just have to man up and ask the question. I know it is tough putting yourself out there for rejection, but even if she rejects you it doesn't mean anything, she is one fish in a pond of many hundreds. And most of all, you have to remember it is her loss, not yours!