I think I see what you want to do.
Currently you have your laptop setup as dual screen, you laptop screen is #1 and a monitor on the kvm is #2. But screen #2 is also the only screen for the pc and you want to see that in dual screen also.
First your pc's Video card (GPU) would need to support dual screens. Otherwise you'll be buying a new GPU.
Second is you dont need to buy a new KVM.
You might wonder why but if you think about it then you'll realize that your laptop can't do triple screens so if you bought a dual KVM the third screen would just be black from lack of input. So using your existing kvm, and buying / adding another monitor to the pc your setup would be:
Laptop monitor + monitor on KVM + pc monitor #2
Pressing the KVM switch would cycle one of the standalone monitors between the laptop and the pc. the laptop display would always display the laptop and the third monitor would always display the PC. So you'd be looking at screens either:
Laptop1+Laptop2+PC2 or Laptop1+PC1+PC2
Am I understanding you correctly?