Check out Kut Kwick. They have what you want, but bring some money, they ain't cheap. They're used in forestry, State roadside departments. Last I checked they had decks going into 96" and larger. Diesel powered, hydraulic activated, cab with a/c and heat. Built like tanks.
Edit: I was incorrect. They use a 88" deck. Check out video of Ground Master doing its thing.
I have an older model Kut Kwick CL20-60(probably a picture of it will come up if you type in the model #) from 1990 using an ONAN 20 Performer engine with front 60" deck. It's a rear steer model that was changed in '91 to a different style. It will take down saplings 1" easily. It's 12' long and weighs around 1200#s. The deck is made using 1/8" plate steel and it alone weighs about 400#s(with accessories) from what the company historian tells me.