Look for a front axel out of a 55-59 Chevy/GMC 1/2 ton pickup. A friend of mine (who has one under a 33 Chevy) suggested one for my 34 Master. He said it is the same width as a 34,(he had to narrow it for his 33), so it probably will work for a 39 too. To have 5 lug hubs, look for 51-54? Chevy p***. car front hubs. I'm not sure if the springs will work though.
I think that in '39 the Master had independent frnt suspesion,but the Standard models had the beam axel. The front axel from a '37 or '38 Standard should be the same. You'll also need the brackets to attach the beam to the frame. The brackets are riveted to the frames on the Standards and are removed by drilling the rivets out.