Looking for a tricopter YAW mechanism, with a metal gear servo.
Not up for trying David Windestal's nose wheel steering mechanism idea(have tried and failed miserably at that).
Please pm or whatsapp me on +918967922034

Would this work: http://www.quadkopters.com/product/diy-parts/easycopter-tilt-motor-mount/ ? You can add your chosen servo to it.

do not use a metal gear servo - they develop slop very fast(unless you are planning
on spending big bucks)
for a normal sized tri - a HXT900 is adequate.

look around the robotics forums - I would suggest a pulley driven
toothed belt with the servo located inward (or a pull pull mechanism)

this way when you hit the ground - your servo is isolated.

you get the added advantage of more equal weight distribution.

tris  are my favorite type of multirotor and I'll post pics of mine in a couple of hrs.