My black tri dog's coat has faded on his rump and desperately need to find a shampoo to bring the rich black back again. Can anyone help?

If you're showing him then you shouldn't use anything to change the colour or texture of the coat.  :)
That's what happens when black coats spend time in the sun.  Most are kept out of the sun both or that reason and because black dogs tend to feel the heat.
His new coat will come through black again. :)

He dose not lay out in the sun and like a normal dog he has a life so he goes for a walk over the woods every day. He is sprayed with UV protection but I do not think that  is that good.

don't think you would be allowed to use it if showing but ive see sprays and shampoos to darken black coats at some shows, don't rember and of the names.