I have big LPL mouse trap shutter, big enough to be a rat trap shutter, which is currently acting as a lens mount for my 36cm Heliar - As soon as I get a simple flange and extension so the rear elephant of the Heliar clears my Sinar Shutter, you are welcome to it for a fair and sensible price, whatever that is
The LPL shutter is the thing between the lens and the lens panel, the lens mounting screw is integral to the shutter, actually machined into the front of it
Another option is a Shanel Nr 5 shutter - I kid you not, it is a Rittreck made shutter for rear mounting behind a barrel mounted lens - Mine came with my 420mm R-Claron - As I use a Sinar shutter for most 10x8" work it is sitting in a cupboard
Our digital camera is with my wife in town at the moment, so I won't be able to send pix until after 3.30 this afternoon