Jay Newirth (of newSOFT) is selling a Model III power supply using modern power supply components while retaining the use of the existing wiring inside the various Model III computers.
Available options are 1 board or 2 boards.
For more information contact Jay either at JAYNEWIRTH@VERIZON.NET or visit his website at NewSoft Store.
The Model III uses 4116 chips. These are still generally available although you need to be careful of the source. Fake chips (or chips that will fail) are very much a risk, so it is important to source them from someone who has run them through a RAM tester. There are people who sell based on how much they have on hand, and you can always try your luck on eBay.
If you need a replacement badges for your Model III, NewSoft sells them for a very reasonable price.
Matt Boytim is developing a small board which can be used to replace the keyboard and/or monitor of a TRS-80 Model 3 and 4.
The project, which can be found at this GITHUB will permit using a PS2 keyboard and/or a VGA or HDMI monitor.
Matt has advised this is still very much a work in progress.
Power Connector Assembly
If you would like to use a standard computer plug instead of the one permanently fastened to your Model III, Newsoft sells a repalcement power connectory assembly. Note: Will require you to open your Model III and do some disassembly and re-wiring.
If you would like to repaint your Model III, you might want to read the How to Paint your Model III or 4 guide by Patrick Bureau, downloadable Here.
For hard drive and floppy drive replacements, visit:
Jay Newirth has discovered that the Everbilt 825 031 Rubber Bumpers are an excellent replacement for the feet on a Model III/4/4D. Jay recommends using washers at the bottom to avoid the screws digging into the feet.