Hello!
I'm afraid you have to build one yourself... You take the chassis from an AMT kit if it is to be American and from Italeri if it is to be European. Then a lot of plastic plate for the top...
Could you post a picture what it is supposed to look like?
Funny thing, trailers are so much harder to get than the tractors for them. Around 2008 there were hardly any trailers to be had, fortunately around 2010 AMT reissued their trailers, that helped a little.
Good luck with your projects and have a nice day
Paweł