That's an older Peggy hair. I love that hair. <3
Peggy's site doesn't always display correctly or at all in Google Chrome, so you'll want to try the link in a different browser. (Safari, Firefox, Opera and IE all should be fine)
In the future, if you can't find a hair, MS3B is obviously a good place to look, but I realize it's hard to search for older items. The TS3 Hair Gallery, here: http://simswiki.info/wiki.php?title=TS3_Hair_Gallery , is great. It might not have the very latest hair, but for anything slightly older, it's the best resource.