Old braille computers

I realize this post is off-topic, but I don't know of a German list to ask this question. I also only know English. Does anyone know where I might find a used David 486/Pentium or Notex486? A David 386 would be fine as well. I will be teaching blind children braille and computer skills, and I thought it would be a great notetaking tool for blind high school students. It also might help with teaching braille writing. Thanks in advance for any answers. You can write me off list since I know this question is off-topic. Thank you. Leslie Fairall