Simon, The arches you posted in your link are commonly called 'monte carlos'.
(refer to the white roundy in the pic at the top).
You can get some from Josh at miniimports. He shouldn't be too far away from you.
In terms of whats easy to fit and what's not I can provide a little light.
Fibreglass arches are a bastard to fit. I bought some 'old style' wood and picketts in fibreglass and couldnt get them on my carwitout lots of stuffing around, so I bought some monte carlos a few weeks ago. I've only put the front one on, but it was pretty easy. Being plastic you can trim them easily and drill where you need to (fibreglass shatters if you arent careful and the dust is annoying), and a heatgun will sort out any other issues.
Generally speaking, any arches that have external screws are easy to attach regardless of what they're made of, as the screws are always at the top and pull the arches into position.
For the record, these are the 'old style' wood and picketts I referred to. If anyone knows their actual name or manufacturer I'd like to hear it, but my guess is the best I have!
They look like montes at first, but they don't get cut off at the bumper, instead continuing further down and blending in a bit.
