All you need to do to replicate Subaru wrc decals is buy a Subaru wrc body from Tamiya. That's going to be an already accurate body with the most scale-accurate decals you'll ever find.

If I'm not going that route, I usually go with decals that come with bodies/parts. I'm not a big fan of paying money to display company logos on my cars - full scale or rc. I've contacted companies and asked for decals before. Good companies will be glad to hook you up. It's a twofer. Helps your vehicle look cool, and gives the company some exposure - at no cost to you.