You could actually get away with just having the front and sides and not having a rear. It looks okay.

As for your dilemma for finding the front and sides. I guess the next best thing you could do is call up jdmshit.com and ask when they get their "mugen v2" lip (which looks like the the WW RS lip) in stock so you could get those.

For the sides, you might want to call up pann auto @ 858.278.7266. They might have some older WW stuff in inventory that you're looking for.