Does anyone know of a source for more of the "Watch Mr. Wizard" episodes (the black and white ones)? A few are on YouTube, a selection was made available on DVD

Does anyone know of a source for more of the "Watch Mr. Wizard" episodes (the black and white ones)? A few are on YouTube, a selection was made available on DVD (since out of print and quite expensive) but I have found no others. According to his Wikipedia page he filmed 547 episodes but only a handful are still accessible. I ask mainly for my son who keeps asking to "watch a Mr. Wizard video" and who is well into reruns of what is available on YouTube.