There are hundreds of comapnies that pre make drawers, door and cabinet parts. I go to the Manifacturing fair everyother year. They really don't sell sevral at a time. They take orders for cabinet shops. Most of the makers of parts will not deal with you uless you have a business lisence and they have minimum orders.
They are companies that make metal drawers as well as wood. Anyone with a good used $150 Delta or Craftsman contractors saw can build them. I have built thousands of them for cabinets I have made. I am an architect and general contractor. I ran a full scale cabinet and mill shop for all my comercial needs. I made custom built-ins and furniture and still make custom furniture.
Any cabinet shop can make them up for you. The problem is that these company's make them so cheap that the cabinet shops buy them cheaper than they can make them.
I have 4 shapers but I buy all my doors for cabinets. You can buy any style, size or type of wood you want. I have made many cabinet and entry doors but the past 35 years it is so much cheaper to buy them. They are labor intense. I can get many more jobs done when I don't need to shut down to make doors.
A good small table saw will make you all the drawers, dividers, socket trays and holders you will ever want.