I have done some small run table and hanging lighting, employing single bulb corded sockets, and was referred to a contract lighting company out of the greater NYC area called Glucksman Lighting (look them up with your favorite search engine). I assume there are others like this elsewhere in the country, but they aren’t easy to find.
I contacted them to have some UL compliant lamp setups built to my spec, though to offcially UL “list” said lighting setup (assembly consisting of the cord, switch, socket, et al) was an extra per-unit cost, that I declined at least for the initial run. They even spelled out that the listing itself is mostly just paperwork and record keeping on their part, the physical product is assembled no differently listed or not, but there is definitelysomething to be said for personal piece of mind and less legal liability. They do have order minimums and their UL listing only covers the electrical portion of the product they are putting together, not the lamp shade/stand/structure that you are connecting it to, though I am unlear if that is nessesary, perhaps someone above can clarify?