NPD, or
www.CJponyparts.com, or
www.californiamustang.com, or
www.mustangsplus.com, or
www.mustangsunlimited.com, or
www.laurelmountainmustang.com, or... well, you get the point.
I bet they'll put it in an envelope if you ask them, instead of charging you 8 bucks for shipping.
Or, go to the local parts place (O'Reilly, Autozone, etc.) and see if they have a tee you could replace it with. You can just make or buy a little sheetmetal bracket to hold it down. Might consider replacing the lines too, if they're that brittle.