Yarn Donations for Community Service Project?

I am the project lead for a community service project at work. Everyday MLK Day we close our office to donate the whole day to serving the community. I am running a knitting group! We are knitting scarves and hats for the youth and elderly in the Philadelphia are. Anyone have ideas for where I can find yarn donations? I am looking for worsted weight yarn in any color and any amount!

Thank you in advance!