Briant (the manufacter of the "apron" distributed by Bagster in France) is imported in the UK by Baglux. More expensive than Steptoe's beautiful solution though (although it looks less like a floppy shite bag, more like a shite wrap due to the stronger rigidity of the leather-like material), so it may be worth or not the extra money, depending on your taste and income).
They say it costs between £102 and £165 depending on model (it's a GS specific model too). http://www.baglux.co.uk/apronsandmuffs.php.
It's in the "Briant" section.
Anyway, if I was concerned with aesthetics, would I have bought a GS?
I find my bike beautiful, but sometimes I think I'm like the mother of an ugly baby...
Mine has fully adjustable inflatable sections to stop flapping at speeds, fully insulated with large internal pocket, when you see and feel one you can tell it's a quality item - the same makers as the fantastic handle bar muffs that everyone raves about - And it comes with a storage bag, for when it you put it away during the summer
Here look under GAUCHO R117 fits the GS ( £75) - the handle bar muffs for a GS are R319 (£28)
Sorry Steptoe, no offense meant. This was just meant as providing an alternative product. As I said, it's a matter of taste (ie one can prefer one or the other, visibly most people here prefer none!). I think it's a very subjective matter. I was not in any way implying that the Bagster solution was a better product, I was just saying that it was more expensive (a fact) and more rigid (my mistake, I didn't know you could inflate the sides of the shite bags), and leaving it to everyone to make up their mind. I can even go further: had I known at the time of purchase (2 years ago) that your solution existed, I might have got one of yours instead!
Again, please accept my apologies if my imperfect use of the English language may have sounded derogatory to your high quality product (no irony here).