The sad fact is that most labs have either gone digital or gone bust, this means that there a lot of experienced people out there.
Your best chance may be companies/organizations that have picture libraries, especially those whose pictures are likely to be large format.
When I worked as a printer we did some work for Rolls Royce(Bristol), it could be worth calling them, they had an extensive archive.
With the way things are moving I suspect that any work with photo libraries now would be transferring the images to digital.