Regulating voltage at end of 200 foot 120 V AC extension cable
To directly answer your question: what you want is a "voltage regulating transformer". Alternately, I have also seen the wording "voltage regulator converter transformer" - basically add "transformer" to the search terms you're already looking for.

The issue is, in order to counter the voltage drop, you need to start at a higher voltage, so you need a transformer before the regulator. Likely you will need a 240/120 V step down transformer (most common). In theory there could be a  110V/120V+ step up transformer that will do a slight step up before the regulator so the regulator can regulate it down - but I can't find a specific commercial device that does that. Hopefully there's a 240V plug available to you, as well.

That being said, you should take the comments that have been made into consideration. It's likely much cheaper to just get a thicker extension cord (especially consider you'll probably at least need a new 220 V cord for the transformer anyway). The bigger the conductor cross-section, the less voltage drop per foot you'll experience. You can do the calculations to figure out what size you need, I suspect 10 AWG as was suggested will probably be sufficient for 200 ft.