The smaller a servo gets, the more expensive it can be and better the quality is needed.
These are a very nice 12 gram servo by E Max.
Type: ES08MA II/ES08MA V2
Size: 23 x 11.5 x 24 mm (1.25 x.45 x.94in)
Weight: 12g / 0.42oz
Working voltage: 4.8V~6.0V
Working current: 200mA/60°
Speed: 0.12sec/60o at 4.8V; 0.10sec/60o at 6V
Torque: 1.6/2.0 kg.cm (4.8V/6v)
Materials: Metal Gear
The line length: 25 cm
Standard: Futaba/JR universal plug.