Easiest place to start would be to pick up a Renault 4 Frog. That would provide the front and rear wings and the hood.
Though the early factory workshop manuals have a lot of information about how the Renault 4 Plein Air was assembled (there's just about enough in there to show a dealer how to convert a standard car to plein air using factory panels). eBay.co.uk often has the manuals. M.R.61 is a manual with the information.