Quick flirting

Ask him before he leaves as long as you've talked to him a little. You can always just be like, "So... we should hang out some time, how should I get in touch with you?"

Or you could try asking him straight.. probably near the end of the meeting, but make sure the conversation has really got going first or else it'll seem a bit desperate. Guys are pretty simplistic. I'm sure, that to get a guys number, it doesn't require as much BS as it takes to get a chicks number.

Be like....."so maybe we should hang out sometime..." see where that leads the conversation and he might actually be the one to ask you first. It happens like that with me sometimes. I'll ask that and he will be like "oh yeah that would be fun....do you think I can get your number so we could plan something?" I hope that helps. Good luck with that.

Ask him some random thing (How do you like this party? What's your favorite drink at this bar) and listen to his answer, using body language to show him you're listening. Just keep asking him questions. (You like the Berry Bomb? What is it?) If he mentions a personal interest, ask him about that. Continue with the asking questions thing--whenever he mentions anything question worthy, ask about it. When the conversation is definitely good and he seems animated and interested, say "Sorry, I've gotta go, but I'd love to talk to you again sometimes." Pause. If he doesn't ask for your number, say, "Let's exchange numbers." When you've done so, say "Call you soon!" and walk off.

Remember that body language is key here. Most flirty words sound ridiculously stupid, but whispering some things to him, leaning in to him, playing with your hair and licking your lips--those are subtle enough not to look desperate and obvious enough he'll be able to tell you're flirting.

BTW, if this works out for you well, he'll probably be asking for your number.

"Hey, what's your number? (... just in case I don't see you again.)"

Say, "what's your number?" :)