Plastic Micro Servo Adapter for LEGO Cross - 16mm long : ID 4252 : $0.75 : Adafruit Industries, Unique & fun DIY electronics and kits
Amazon.com: Build MISINI 27-Piece Set CADA Power Functions Pro, High-Speed L/M/Servo Motor Set (Including Cross Shaft), 2.4G Fast Charge Remote Control Battery, Compatible with Lego Technology Cars : Toys & Games
Adapting Servos to LEGO – Brown Dog Gadgets
Amazon.com: New Lego Power Functions Servo Motor (88004) : Toys & Games
LEGO® Power Functions Servo Motor 88004 | Technic™ | Buy online at the Official LEGO® Shop US