More than likely the furniture company has had those brackets made. They wouldn't have to be L shaped. You could purchase some 1/4"x6" flat steel and make your own. It would probably be even better with more surface steel. The steel can be cut with a metal cutting blade on a circular saw and you could drill and countersink the holes with a drill press. Even though with that design I would put air under the table any time it is moved. Without a skirt there would be a lot of stress on the joint.