I sold off my Leica iiic years ago and went digital. But I'm cleaning the closet and found 2 cable release adapters; you need these to work a regular cable release on the iiic (and probably most of the screwmounts, but don't quote me on that). If you're in the US and want them, send me a message at morthcam58 at gmail dot com and they're yours. I'm not going to bother taking a picture of them, here's what they look like. They're free, no returns, refunds, international or overnight shipping; first come first serve.
Thanks