I was just on the Australian Houzzers say Hi thread and I noticed a post from Deeane Raphel in the U.S. She may be able to arrange shipping. Good luck. Ps Have you visited an agricultural or shed shop? You may have to visit as they don't always have an online presence. They may have the fixtures for a barn door under another name.

There are DIY barn doors on Pintrest. I like your idea of cladding an existing door but I'd source the hanging hardware first. There may be thickness limit. Good luck.

In my last house, after adding a living room (the area you see this side of the arch) and also updating bathroom etc I couldn't afford to reline the ancient walls in my little lounge (when I removed the purple wallpaper I found a mixmax of boards, gib, pinex, plywood and holes!) so I plastered walls all over with layers and layers of newspaper and wallpaper paste (papier mache), then after applying primer/undercoat I painted with 2 similar colours (rich reds in this case), and stippled the surface with a plastic bag. This made it look just very slightly textured like leather and successfully disguised the uneven surfaces. Gallons of gap filler filled the gaps between the old T&G ceiling boards and evened out the mismatched skirting and scotia. Again white paint on all the trims. Amazing what can be done when you have to make do! This was a great cosy little room! (Before photo is the 3rd one)

Hi Dr Retro, Thank you. I really appreciate the input and the time you've taken to explanation your point of view. I really do want to get an understanding of where the issues lie in this design. So I hope you'll forgive me digging a little deeper. I don't quite follow why you think the design would require a 6m lintel. Yes, it does require a 6m track, but the track can simply be attached to the wall. The weight of the door need not be supported by the top track. It could be supported from below. The whole point of putting the configuration on the outside of the wall is to minimize the need to make structural changes to the building. There currently is no capacity to install a 6m wide external sliding door/window unit. Likewise I don't follow why the door should be any draftier than any other external sliding doors. The cavity is on the outside of the wall, so draft is not going to get in via the cavity. Other sliding doors of the unit type have the same draft problems this configuration would and solve it by using an overlapping flange at the front end of the fixed door and the back end of the slider. The same could be applied here, where we treat the wall as the fixed door.The point at which the doors engage each other has also be solved for other door configurations. It is just a matter of having a loose tongue and groove configuration. Again this is exactly the same as a unit providing center opening sliding doors. Finally the same sliding mechanisms are used in other sliding door configurations, so I don't see why that should be any draftier here either.