Here's an example, there are others that offer a strait side replacement rather than the concertina type. Might be worth a call to see if they can make one to match your original.
The Weathershield concertina poptop, as used on the Maidstone was also fitted by Holdsworth on their Commer Super models. A replacement concertina bellows is available from poptop-parts.co.uk as posted by Panky, but its the Devon roof page, not DanburyNot cheap at £599, but you can also get a plain white bellows at £449. I believe that they make a plain white canvas (non-bellows) for £149. They also stock the headlining, roof rubber seals and vent.
justkampers.com have quite a few bits for the Weathershield roof as well. I bought the 'J' seal off them which is the seal between the poptop roof edge and the Commer metal roof, price was £24.95
I started with nothing.....and I still have most of it!
When i bought the van the top was in pieces with no rubbers or instructions on how it all goes together.
I got onto a mob called www.justkampersaustralia.com as carcamper mentioned who said the roof profile looks alot different from there's.
How does the bellows attach to the roof on our vans? is there a diagram on fitment.
With the plain white canvas would this type fitted to the concertina frame get tangled in the mechanisms?
I havent got any tail lights but in the past I have found them cheap on ebay by just putting that part number ,they were fitted to a lot of british cars or just keep an eye on rootes spares as they get listed there too
Is this what you are looking for?
http://www.ebay.co.uk/itm/NEW-HILLMAN-ROOTES-HUSKY-MINX-GAZELLE-REAR-L572-LAMP-/400385501923?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item5d38d5eae3