David, you should be able to find both the Owner (only go for the F Tool GP-60) and the Duo if you shop around. I'm pretty sure if you check with places like Proshop Mogi, you will find them. The Owner will be around 3600 to 3800 JPY and I expect the Duo will be 6000 to 7000 JPY.
I have owned (or still own) just about every plier discussed so far in this thread including the big 8 inch Accurate pliers with the split ring jaws. From my experience, I like the Owner GP-60, Duos and Ocean Revolution as they open big split rings like the 11H and Varivas 400lbs easily. The Duels are also a very good pair of pliers and have the added advantage of having a small pair of jaws as well so they can be used for smaller split rings too. There is a bit of a knack to be learned using these but they do the job very well.
As far as the Accurate goes, a great pair of pliers but horrible split ring jaws and I don't regard the Fisherman as much better. I do know guys who swear by the Fisherman but (sorry Hon-Su!) side by side with any of the pliers above, it just isn't in the same class for big split rings.
If you are going to get a lot of exposure to salt on the pliers, I think you should probably discount the Owners unless you are prepared to continually lubricate them. They will seize up with a couple of days. For your purposes, I'd suggest you look at the Duo.
Thanks for all the replies. What kind of prices am I looking at for the Duos or the Owners? Sorry, I'm having trouble finding these for sale online (like Owner doesn't have them on their site).