Hello Mustang and welcome here,
Do you have a specific modelling project ?
There are excellent drawings of all those Renard fighters in the book by Nicolas Godfurnon Renard R-36/37/38 & 40 (bilingual French / English), published by FNAR:
http://www.fnar.be/?Livres:Renard_R36%2FR37%2FR38_%26amp%3B_40_by_Nicolas_Godfurnon
All the versions of the R.36 to R.38 are depicted in both 1/48 and 1/32 scale, and there are numerous technical drawings. Front views of the R.37 and R.38 are strangely missing, perhaps a mistake when the book was layed out. The 1/32 drawings are unfortunately overlapping facing pages, with the book hinge in the middle. The 1/48 drawings are unaffected, and should be enough for most purposes.
I'm sorry I will not post scans of those plans in the forum because the book is still available new and the set of plans makes a good chunk of it. But if you are seriously interested in those aircraft, I can guarantee that you won't regret buying it.
There are drawings of the R.38 in the book Les avions Renard by Hauet and in other articles, like that posted below from Avions no.153. But the plans by Godfurnon seem very carefully researched, and I would rather use them.
By the way, maybe you'll be interested by this post listing other reference books about Belgian aircraft:
http://www.secretprojects.co.uk/forum/index.php/topic,19339.0.html
Cheers,
Adrien