I just went and looked at two Nikon view camera lenses and they both have tapered threads in the shutter release. In addition,in my drawer of "camera bits" I found two shutter release cables with tapered threads. Certainly at one time they were as common as dirt as I certainly don't remember having any problem in locating them.
If that is what you are looking at try locating a camera shop that deals in professional cameras and give them a call.
Bruce in Bangkok (brucepaigeATgmailDOTcom)