Theres a small group of us that has modded our Jazz and most of the parts were sourced by Matt at Injection Imports which werent cheap as I've mentioned before.
We met last year at Bluewater Mimms and were able to get inside slot as as you said, you dont see much modded Jazz.
I've noticed a company on ebay selling a replica Mugen kit so maybe worth a try ? Not sure on fitment though.
My Mugen kit was sourced through my local honda dealer who were authorised reseller of Mugen Europe which costed me a fortune