I realised when I reread your original post just now that you actually said GRP, so not a surprise. Anyway here's the pic of a nude 968 I knew the existence of (thanks again Stu):
As for how I did it - well I bought the rear sections as desribed above from Simon B, exhausted the options for used front bits and ordered new ones via OPC Exeter along with the fitting kit and rubber edging. I then gave the 4 PU parts to my preferred bodyshop to paint Glacier blue. When I got them back I was probably £300 into this project and that was when I discovered that they weren't going to fit straight on [
].
I then positioned the trims using tape and drilled through some minimal holes to hold them on, and discovered that they
still didn't fit because of the moulding behind for attaching the clips, so I trimmed that off with the Stanley and fitted one of the rear sections flush with the car. Then I offered up the front and discovered I had to cut my wings. I appreciate that with all the people who have crunchy wing bottoms it was borderline criminal to do that.
It wasn't especially difficult, nor even time-consuming in the grand scheme, but it was a classic case of what started out as a simple plan turning out not to be so simple, allied to a case of "well, I've come this far..." I actually really like the look and I guess not many people would go through with copying it so it will stay fairly unusual, although I suspect you aren't worried about that.
Sorry, I have no idea how well GRP replicas are made or fit, but at a guess Simon at ESS could get some, and maybe Club Autosport do them, though in that case I wouldn't bet they fit any better than the genuine ones. I would say that mine being flexible is a real boon - they are pretty scuffed underneath from brushing kerbs etc. as they ground long before the front splitter, and in GRP they might be cracked, though they hang down below where they really need to and if they were snug to the sills at the bottom it might not be an issue - I like how low it makes the car look though.
edited to remove a spurious "I" at the end of the original post and to add thanks to Stu C-S for the pic.