It is. You can find it in cans or cartons, but a lot of stores don’t always have it stocked in much quantity. The good news, though, is that you don’t need it. All you really need is the salt water solution (1 cup salt per 1 gallon water), an optional sweetener (sugar, brown sugar, honey, maple syrup – about the same amount as the salt), and whatever spices you might want to try (peppercorns, cinnamon, whatever takes your fancy). Some halved lemons or oranges are also an option. You can also make Alton’s brine recipe substituting chicken stock (low sodium would probably be better since you’re adding a lot of salt). As lomg as you get your water to salt ratio right, it’s hard to screw up a brine. You have a lot of freedom to be creative.
It should be, especially if you do it in a bag. I’ve never had a problem. If you don’t end up with enough brine, just make another quick gallon of salt water. One thing you should NOT do is just try to top it with plain water. You need to preserve your salt ratio or the brine won’t work, and you’ll risk your turkey going over to boot.