Try Servo City. Here is the link...

One link is for all servo arms they sell and the second one is for some heavy duty DuBro arms that fit the HS-85. I have used these before on other Hitec servos and they work well.


http://servocity.com/html/servo_arms___horns.html

http://servocity.com/html/hitec_heavy_duty_horns.html