If there is a floor flange available in a 1x2 dimension, it's probably going to be pretty pricey, especially if you need a few. There are dozens of ways to accomplish this task, depending on exactly what you are trying to do. For a quick DIY, you could use the corner braces shown in your first link. A pair of them, on the wider dimension of the upright, would actually be pretty substantial. Beyond that, there is the possibility of both gluing and screwing the joint together, or even using a Kreg jig to drill a long hole in the "leg" which would allow you to bury a screw in the upright, and firmly attach it to the base. You would be amazed at how a single wood screw, drilled and installed from under the base, up into the leg, with a few dabs of yellow wood glue, can result in a rock solid joint.