Dubro used to make a simple nosewheel brake part #157 .. Just a drum that tabbed into the wheel with a coil spring to apply friction when a cable was pulled..

We hooked it up to the elevator servo .. down elevator applied the brake.

Rocket City was making them but they folded.

You can sometimes find them on Ebay.. ohh like right now.
There is one in this lot of parts.

http://cgi.ebay.com/Rc-airplane-land...QQcmdZViewItem

Hobby Lobby sells an electric brake from kavan but it's $57 Pn HLFK263