Bill Keough (Keough Hackle) also markets a cape similar to the Whiting American Hackle capes at about the same price, which he calls Saltwater/Bass Capes. They are not as easy to find as the Whitings capes though. Hugh Spencer (Spencer's Hackle) also sells capes and patches that would be suitable for tarpon flies. Pretty much any cape that will tie large salmon and steelhead flies will work. I would look for any of these three hackle growers capes for salmon/steelhead flies.
Avoid the Chinese hackle capes because the ones on the market are small these because of the bird flu causing so many of the birds to be killed that the ones left are small imature necks.