I was at Home Depot last weekend . . . one of our lamps stopped working, and Lamps Plus did NOT have any parts. The salesman looked me straight in the eye and said "We don't sell parts." Pathetic, IMO. A place that calls themself "Lamps Plus" does not sell any parts.
So I headed to Home Depot, which was just a few miles down the same road
They had exactly what I needed, for about $6 . . . the part where the bulb screws in, with the twist on/off switch
I also noticed they had just about every imaginable part needed . . . cords, switches, sockets, brackets, lamp shades, etc. They even had plenty of "make it yourself" lamp kits