I carry an aluminum copy of the Jack pictured above. Notice that it uses two opposing blades. I'm not positive the blades are stainless, but suspect they are, due to the fact that mine has spent the last 4 or 5 years in my paragliding harnesses and the blade still looks shiny new. My paragliding harness does not touch saltwater, however.
When I first got the knife, I made a sleeve for the inside of the holster. I just folded over a piece of cardboard that I had soaked in motor oil. The original idea was to ensure that the knife came out of the holster smoothly and quickly, even if pulled from an odd angle. The oil surely helped with longevity too. I'm thinking I might now want to pack the holster with vaseline for it's new life in saltwater. To keep that from turning into an oozing mess, I'm going to try replacing the cardboard liner with a plastic one.
I got the knife from Kevin Lee at Thermal Tracker Paragliding in Grants Pass, Oregon.(US) It was about $30.US if I remember right. He has another model that looks interesting too. That one has a handle that closely resembles an oval caribiner, but has only one blade.
Thermal Tracker Paragliding and Aero-Sports
1920 North East D St.
Grants Pass, Oregon, 97526