Creating Subnetwork in present flat

I have a 10.2.0.0/16 Network. I have 2 nos. Layer 3 6506 Cisco switches. Right now no layer 3 subnetting is done. It is a flat Network. Now I want to further do subnetting as 10.2.x.y/24. I require 26 subnets or VLANs. What is the best way to migrate to Layer segmentation so that my internal and external communication goes on. My external network is 10.0.0.0. Can you help me out?