Yes, the “assemble available components” route is the one Roger hoped he could go down. As I suspect Robin also found though, given his use of Meccano & Jubilee clips, the solution to the problem turned out not to be that simple, particularly in the case of obtaining a wide FoV. He thus had to engage in some creative engineering metalwork (and a crash course in silver soldering!) in order to make everything (literally!) come together.
Given the lack of immediate responses saying “oh yes, I got one of those ages ago”, it would seem there is indeed no commercially available unit of this specification available, which answers the first part of Roger’s query which I posed in my original post. As to the second part, while he is sure that such a unit would be of great benefit to the beginner, the fact that constructing one is not straightforward leads him to suspect that, now he has (he believes) come up with a workable solution, it is only really a commercial manufacturing process which would be able to build them to a reasonable standard in reasonable numbers. Hence his appeal to members who might have contacts with such an enterprise (or possibly a hot line to BBC’s “Dragons’ Den”!). Anyone able to help?