i love writing with a quill!!!! I might even use it in school next year...
I got it at the House of Seven Gables shop in boston, but that is a lot closer for me than anyone else here....
I would suggest anywhere that is a historical site, ive seen them all over those places, specially gift shops.

To make paper look old, you can always but it in the oven... You wet the paper slightly with a wet tea bag, and then put it in the oven at like 200 degrees F, but you need to watch it, cuz it doesnt take long at all.
DISCLAIMER: Its not my fault if you try this and it doesnt work, or if you get hurt, maimed, or die in the process... this is only a suggestion