Are you looking for both a leaf shutter and a focusing helical? If so, you will need something like either a Bronica or Hasselblad lens for their cameras that have no focal plane shutters, or something like a Mamiya lens that is intended to be used with one of their focal plane shutter cameras.
A C330 or RB67 lens has a leaf shutter, but needs a focusing mechanism.
One thing you will need to figure out is how to deal with the shutter cocking and double exposure prevention mechanisms built into these lenses.
The leaf shutter lenses for the Mamiya 645 cameras might be a good choice. They are designed to be cocked by hand, and are set up to be usable with stop down metering. The older, 70mm version can often be obtained at reasonable cost.
These lenses can not, of course, be counted on to cover formats much larger than they are intended for. In addition, if you are intending to use a lens intended to be used to cover a rectangular format, you may find that they won't cover the equivalent square format - they are sometimes internally baffled to minimize flare.