xscope wrote:
If it's going to be so difficult to find a nut that will fit (i.e.
getting someone to make it for you, having to raid a museum etc.), how
about changing the bolt in the tripod to one with a more modern thread?


We have lots of Whitworth bolts and nuts, from 1/8" to 9/8"
Here's a picture of them:
http://tinypic.com/wrc6zd.jpg

and can easily get more from the shop, although Whitworth costs a
bit more than UNC.
We also have a large range of Unified and Metric nuts and bolts.