I've gone down all manner of weird and wonderful avenues (British Library, Patent Office Library, now part of the Brit Library, and the Science Museum Library) and - incredibly- none of them has anything other than the same potted illustrated books one finds in Ian Allan bookshops
It may be stating the obvious, but the format in which you're most likely to find Maintenance Manuals, IPCs, etc for the Trident isn't hard copy, it's microfilm.
That's certainly what we were using in the hangars by the time I was first let loose on Tridents (early 70s).