Hi,
Being from Belgium - the real home of Tintin - , I'm very happy to hear about your project. I've been thinking of doing that Moon tank for a while but still haven't got to start it. As far as I know, there's no kit for it (if there is, I'd like to know), although one can find various replicas in the Tintin shops worlwide. Expensive option, though. And there's no pleasure in that, for a modeller!
If you are into scratchbuilding, and interested in another Tintin tank, the one he drives in 'The Calculus Affair' there's a good article at
http://modelbox.free.fr/dossiers/tintin/BordureChar_P/
If you have trouble with the French language, let me know!
Sincerely,
Domi