I have a solenoid with no conecting linkage (just the threaded post that comes out of the end). Do I have to search/scrounge for a new linkage, or can I fashion something on my own. I've built some RC cars and planes before and it seems to me that this is not much different than a servo linkage.

Obviously the correct linkage will be the easiest route. Fred Lustig can provide the part. If you want to go the self-construction route, the part, for my Optar lens, is essentially a hook. It looks like a flat piece of metal with a small hole in one end [that hole is about the diameter of that post on the solenoid, UNDERNEATH the boss on the end - you'll have to figure out a way to install it], with the other end just a hook to fit over the shutter release.

Once connected up, you have to adjust the position to allow the release to "reset" when released.