where can I buy...

Where can I buy a cammy xbox 360 fight stick?

you can either buy a te and change the art - total cost: 150 or less or you have some make you a custom cammy stick which take longer and be more expensive. Go here for customs Want a custom stick? Come in here! Official custom stick builders thread
and here if you want to buy a stick off an SRK member http://shoryuken.com/forum/index.php?forums/trading-outlet.341/

That pretty much sums it all up. There are no commercially available sticks that is Cammy theme stock.
You have to mod an existing stick or get a custom stick made.

I like to suggest, get a TE, order a Acrylic overlay for the top panel and get custom art printed up.
Maybe some change in button colors and matching ball top to pull the whole thing together.
Art’s Hobbies can do both for you, and I am sure you can find Cammy art from someone here or with some good images searches.

Closes thing to a Retail Cammy Stick is the limited edtion Femme Fatale arcade stick, which is rare.

Only TE stick that are more rare is the Comic Con TE, and the Gold TE which was given as part of the grand prize in a tournament.

I honestly think of Mad Catz made a TE-S for Cammy like they did with Chun Li, it would sell. A Transparent green to match Cammy’s tight leotard, and some color coordinating buttons and ball top.

The closest you can get to an official Cammy TE is to have someone do official looking art for it.