Garage defend and Top Secret.
mainly garage defend, because they keep making it into the news quite often.
Seems a lot of workshops are pretty slow in the development. e.g. Top Secret, saw the car being displayed at TAS but no news of it at all, except that it's for sale.
The current big players in the R35 market are Amuse, Mines, MCR and HKS, none of the other tuning shops have made anything note worthy at all. Must be trying to preserve the factory warranty.