While Lowe's and Home Depot have stock that varies by locale, I seriously doubt they'll have them. They certainly don't in my area.
I am assuming you are looking for SE type sockets (scr.ew-in).
The type of socket you want is called a "Mogul" socket. You can get them online very cheaply, but if you are pressed for time then I'd look for electrical supply houses in your area. Mogul sockets are used for High Pressure Sodium, Mercury Vapor, and Metal Halide lamps, so they are a very common item... in the commercial lighting world. Of course your local home improvement store doesn't cater to commercial, so you need to go someplace that does.
Oddly enough, finding an electrical supply house that is open to the public and will do a cash sale is going to be more of a challenge than finding one.
OOOHhhh... just got an idea... see if you have a Grainger in your area. They'll have it for sure. You kind of have to fib a bit when you sign up for an online account (as they only allow "commerical" customers), but you can order one online and pick it up at will call at your local location. If you want, I can thumb through my grainger catalog when I get to work and post a part number.