I've never heard of them either, and google only throws up Dutch tents, but regardless...here we are.
One possibly-1970s De Randstad canvas awning that came with my '74 Familia. Previous owner told me they'd used it and I've no reason to doubt them. In fact, the photo of it erected came from their advert.
Signs of one or two repairs, sun faded in places, and quite heavy, but usable and vintage!
Has an annex built in for storage, sleeping, secret stash of biscuits, toilet, etc.
Offers in the region of £100.
Obviously there's a bit of weight here. Collection would be better - I'm in the Midlands - though I'm sure a courier could be organised (at your cost!).