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I fear they don't, but with a bit of luck some glamper will be so skint that they put it on eBay.
If you're willing to travel I gather they cost a lot less abroad. missSalaneous (sp?) got hers in Holland, they found it on the net and drove over to buy it, even with the ferry etc it still worked out £100-ish cheaper, and they stayed a few days and made a mini-holiday of it.