A guy in German Brompton forum used to build them for a while in very small batches years ago. Mine is from one of the last batches he made. Very well made, out of carbon The construction is not difficult - the original drawing for the idea is here: http://www.bromptonauten.de/klickfix.pdf It was invented by the creator of bromptonauten.de ages ago (probably in the early 2000s). Another user had access to the machines and materials and built a couple of them and enhanced them a bit over time. Today you could probably also use the bottle-carrier-baseplate that is offered from some asian guys on ebay from time to time. Or you build one yourself.