Sportsman's Den in Shelby is likely to have it.
I say "likely" for a few reasons! First is that I can't be sure because I haven't been there in a good while. (I miss the place!) But I also say likely because this place has a helluva good stock of components and gear for handloading and always has. And lastly... this store has a longstanding relationship with Federal/Alliant/ATK, and if there is any one brand of powder they are most likely to have, it's gonna be Alliant.
2400 is a fantastic powder and a great choice for .357 Magnum. Many reports I have read actually prefer NON-magnum, regular pistol primers for revolver loads with 2400! No worries if you have or wish to use Magnum primers, but don't be led to believe that you need them for use with 2400, as you most definitely do not.
I like to swap brass... and I'm looking for .32 H&R Mag, .327 Fed Mag, .380 Auto and 10mm. If you have some and would like to swap for something else, send me a note!