I would definately say do not get the cheap black repos (Klonkenholm) ones. I did this, wasted £160 +/- and A LOT of my time. Someone told me that arches are the hardest part to fit.
I ended up tracking down original cuts for £250 an arch. You might be in the fortunate position that as we are nearing the summer months, a lot of the importers had or were having their units sent over. Do a search for a thread I started asking for wheel arches (in this section - might even still be on the first page). I am sure I posted who was expecting some arches in May. Also, VW Evolution (who I got mine from at Volksworld), had around 3 or 4 left side arches left. Might get you started?
I have also heard good things about Klassic Fab panels. Whilst they not might be 100%, I bet they are sure as hell better than the cheap repos.
For what it is worth, you do only have three options, cheap repos, Klassic Fab or original cuts/NOS. There was a left hand side NOS one on here and I think the Samba for 450 euro. He was also firm on the price when I contacted him.
If I were you (and me again), go for cuts if you can find them, or if that fails, Klassic Fab.
EDIT: Oh, and all I did was get one of the camper mags and phone every single company in it. I only found one right hand side arch. Made me feel that I found the only right side arch in europe :shock: