Not as long as you might think. I'll have five cans a week some weeks. I try to get decent brands from dollar stores, but I haven't found any in awhile. When they showup, I'll clean off the shelves, and keep going back til they quit stocking it.
I was getting Beach Cliff pretty reliably, but I haven't seen it in awhile. What I suspect, is it comes from the same Canadian canning houses as King Oskar and Brunswick, but are seconds, so they'll stock them for awhile, then release them under the Beach Cliff discount name. They taste just as good as the better brands, but aren't nice whole fillets laid neatly in the tin(Though they infrequently are), They're mostly intact fillets, with some larger chunks here and there to get the weight up. I also like the retro label. It has appealing graphics :^)