I think that Cultural Heritage Resources, the people (Kevin Flude et al) who run the Old Operating Theatre Museum and Herb Garret still organise a couple of guided walks suitable for groups. I don't know if these are only offered daytime.
This is supposed to include a waymarked walk around the area, but the website (still under development and possibly partly done by students?) rather alarmingly states that it will be marked out with "plagues"!
[BTW I had thought I knew most aspects of the "heritage industry" but I have to admit that the existence of an MA course at Central St Martins in "Creative Practice in the Narrative Environment" was a new one on me.]
Am pleased to say that I did get a very nice email from the national trails website - all the maps are up and running again. If you are thinking of walking along the Thames Path, I would certainly recommend this site - in particular it gives accessibility information - one of the things that occured to me when I was walking on Sunday is that some bits would be easy and fun to do with a pushchair or in a wheelchair, but some bits would be impossible:
If you are familiar with the access points and the tides, you can walk all the way from London Bridge to Wesminster Bridge, and on an exceptionally low tide can even get under London Bridge to past Tower Bridge. Sensible footwear obviously recommended, and don't get cut off by the tide! The best area for 'newbie' foreshore explorers is between the Globe and the National Theatre - the surface is firm and there are plenty of stairs. And all the little bits of ancient and modern archeology down there are endlessly fascinating and usually much older than you would think.