You can go to a local hardware store, the mom and pops can usually get them, or a local place like Fastenall if you have one, but I prefer McMaster Carr for all of my fasteners. The site is awesome and they have everything!! http://www.mcmaster.com/#socket-head-cap-screws/=1rr6aj
That's what I've noticed about McMaster. You can get the stuff anywhere else, but it's generally much cheaper. I was going to pick up a few of these to finish up a truck that I'm working on, for the same box of stainless allen socket cap screws that I'd been paying 7 dollars a box for, the local Grainger wanted 16. Thanks, but I'll wait a day for the UPS man to show up, lol.