Your intentions are sound and I think it's wonderful what you're doing. I'm a stickler for written communication so I did a couple of tweaks to your message. I realize this isn't school but my inner writer couldn't resist. Whatever the case, thank you for your compassion to those in need. The world needs more of that.

My version:

"Hi, I'm gathering new winter clothing for the homeless and am looking for somewhere it can be donated and not sold second-hand. Do you know of a location in (my area) that would accept it? If not, do you know of any other charities that would distribute it for those in need? Thank you."