Hi, I think in that scale you would need to make most of those parts, none of which would be very difficult. As for tyres, you're in the ideal scale as you can use endless products from Scalextric and all the other slot racing suppliers.
Cowl vents can be made by push moulding the cowls and joining them to plastic tube of the right diameter and filling and fairing with Milliput.
You really need to find a good book or some sort of reference for the Puffer, before taking on a build of one. I think they're essentially very simple.

Cheers,
Martin