I need to convert 16v dc at 5 amp to 12v dc at 5 amp.

This is Arijit, I am going to use a peltier tec 12706 (rated power 12v 5amp vmax- 15v, Imax- 6a) for a project. My power supply is an old laptop adapter rated at 16v 5amp which fluctuates between 15.5-17v. I came upon these IC 78H12A and LM338 which were perfect for this purpose but isnt available in my area or the internet. Can someone suggest a replacement circuit or ic?

I came upon this circuit with three 7812ct (12v 1.5a max) connected in parallel giving 12v 4~4.5a and thought to do the same with four of these in parallel but most of the online forums suggested is not ideal for steady supply due to power imbalance that occurs if they are connected in parallel. The output current and voltage should be steady so that the peltier works most efficiently.

Any suggestion is welcome.

If you don't care about heat loss and a "non-exact" 12 volts, just use a 1ohm 50watt resistor (actual dissipation 25watts or so)
If you are concerned about heat loss then you will need a buck convertor

I will have a look at the buck converter. Are there any more voltage regulator ic other than those i have listed?

If you want high current you use a voltage regulator chip to drive a pass transistor - you need a regulator with
a separate voltage sense input that senses the emitter of the pass transistor. google "regulator pass transistor"

For your application a 13V zener and NPN darlington on a heatsink suggests itself as the simplest circuit.