Just thought I'd pass on a bit of helpful info. Just before I went on holiday I received a new cover for my Dart 15 that I'd ordered from a company called Goldfinch. It's a great fit, looks well made and best of all only cost me £148! That's cheaper than any other I could find and they claim the material used is 100% UV resistant so it should last a few years.
The only disappointment was that as they're made to order (in Hythe, I think) I had to wait 3 weeks for it.
But if anyone's looking for a cover but is on a tight budget and can afford the wait it's well worth looking at