See below:

https://carkiller.com/scottykilmer/qa/treat-or-replace-headlight-lenses-2007-lexus-es350/#post-82286

https://carkiller.com/scottykilmer/qa/plexus-plastic-cleaner/#post-60125

Find some good condition ones at a junkyard, or buy brand new aftermarket assemblies.

I’ve tried the polishing method for the past 3-4 yrs and eventually got sick of the oxidation reappearing each year, eventually bought new headlight lenses a few months ago (had to go through the process of taking apart the oxidised lens & re-gluing on the new lens. But worth it at just $70 for everything).

It’s amazing how a set of new headlights can spruce up the look of an old vehicle..

There are many different kits you can buy at an automotive store that will allow you to restore the headlights. 

You could go one of two ways; either you can buy a restoration kit and spend some time polishing it (it will eventually fade again)

I had some decent luck using the meguiars Plast-X found in one of the kits for taking off a good amount of the faded material. Works better with a drill and polishing pad.

Or you can go online and get entirely new headlight assemblies (prices vary)