Bad news im afriad.
If there is no dealer stamp to be found, then you dont have a real 172. it probably just a dealer in holland who stuck a renaultsport badge on a normal clio, normally with a souped-up 1.4 engine. It might be worth checking this out with twofast4u, as he has one of the pretend 172s i think.
Seems like there a plenty on fake 172s coming into the country, and none of them have had a dealer stamp in the logbook... probably so the dealer couldnt be traced.
Just kidding...
Saying that, ive just checked mine and cant find anything either. Maybe this is because it was an offical uk car. Will carry on looking to see if i can find it for you.
Cheers
Face