Whilst digging around the internet looking for photographs of the S&D, I came across a Bristol Railway Archive gallery page for Charlton Viaduct at Shepton Mallet, and found four photographs lurking quietly there.
In the index on the left hand side of the gallery page, there is no entry for Shepton Mallet or Charlton viaduct.
Intrigued, I dug a little deeper!
It appears that there are umpteen pages in the galleries that have no link from the station index. Clearly this doesn't make much difference if there are no photographs for that location, but in addition to Charlton viaduct. there are photos of Bath Road viaduct at Shepton Mallet, Radstock North station and the general Wellow area to list just the ones I found today.
The moral of the story clearly is: just because there is no link from the station list in the gallery pages doesn't necessarily mean that there are no photographs to see - use the "search" facility