Here are a few ideas:
You may be better to try to get as close to the heart of the TT as you can, try not to be drawn to the usual stereotypes of all the famous corners and such, but why not get down to the personal level.
Perhaps you could get some very low key and in depth interviews with some of the lesser knowns in the paddock, the ones who will not be the winners but to whom the TT means everything.
You could get out there for practice in the little known places and talk to some of the older enthusiasts who have watched the TT since before we were born.
Look for the rural nature of the course, the huge weight of history that haunts so many parts of the island.
Get in the pub at Ramsey and go out the side door and catch the riders as they pass inches away and into Parliament Square.
Grab a glass at Ginger Hall and ask the people each side of you why they are there.
It is people and history that make the TT as well as those fantastic riders.
If you could tap into the reason so many people are there I feel you would have a very rich human story to tell.