I have Q7 andI want to fit 3rd row seat but my local Audi dealer doesn't want to do it.
I'm not having much luck getting the bits.Who would supply these pieces

 

I'm assuming here that the 3d seat is an option, but you don't have it?
-- So you're looking at the seat itself, belts, seat brackets, maybe some different floor pieces, etc.
--- I happen to have access to a collision parts database, and it has most of the 3rd seat components in it. I just did a rough estimate of what you need (probably missing a few things), and a got a total of $6,314.63 - and that's just for the parts.
---I would suggest that the best way to go is used. Find an auto dismantler that specializes in Audi's, and tell him what you need. Interior items are not in as high demand as sheet metal, mechanical stuff, etc, so you should be able to get the whole set-up farly cheap. You may even be able to install it yourself. Hopfully you're in a large urban area where somebody will actually have a wrecked Q7.

BTW - WELCOME TO THE FORUM!