the mower im working on right now is a gravely 34" ZTR. Its a homeowner unit though...and I don't know if it will fit through a 36 inch gate. I know it will not with the bagger on it, but Id have to do some measuring if you were using one as a mulcher only.
Aries and gravely both made them. Mine is a Gravely ZT-1534. I think they also make a commercial 34 inch, but not sure. You would have to do some checking to see if the would fit through a 36 inch gate.
Here is a link to the Aries:
I didn't see a spec for overall width though.