Unfortunately only Hitec servo arms will work. Tower Hobbies and Hobbico servos are private labeled from Hitec and will fit; however, I am not sure if the are selling arms separately.
We also make new aluminum servo arms. Part number 55701 for the 3/4" single sided and 55702 for the 1" double sided!
Just curious...what Hitec servos are you using?
Airwild Hobbies also has great arms for Hitec and other servos.
(714) 751-7588
www.airwildhobbies.com