Below are some of the commercially available door locks you may want to consider:
Garage Door Side Lock for 2 or 3 Inch Track
National Hardware N280-743 V7647 Side Locks in Zinc
NU-SET 2890-3 Heavy Security Slide Action Bolt Lock
Prime-Line GD 52118 Inside Deadlock
Prime-Line Products GD 52119 Deadbolt Lock, Center Mount with Key Cylinder