Well, the problem in these types of situations is that most guys don't want to get a woman's number, then be seen talking to other women or getting other numbers because they don't want to be seen as "players" or as insincere.
Get over it.
If you enjoy talking to a woman, and you'd like to get her number AND go talk to other people, just say "Here, write down your email and number. I'm going to get back to my friends" and DO IT.
You're only going to be seen as more interesting if you are talking to all the women at the party.