I've actually only SEEN small flocks twice this winter myself, but I've heard many more. If you learn their flight call, you'll be much more likely to pick up on their presence if they're in the area (this is true of all the winter finches, but especially the more vocal or distinctive ones like Ev grosbeaks, snow buntings, and crossbills).
A google search will find some hits, but watch out for recordings of their full song, which you're much less likely to hear (song sounds kind of like goldfinch).
Good luck!
