I added all the .STL flies to the page. This microscope design uses a commonly available 28BYJ-48 Stepper Motors.

Here is a pin out of the coils

Below are some tips if you are looking to make your own.

• It's best to grease the optical tube and gear rack, you will want to ensure there is a good fit and that it moves freely as possible.
• The Pi Camera will need to have it's lens removed to get the best pictures. 
• I found the slide holders on EBAY, on the slow boat from China. (the 67mm version named "Slides Clip Stage Presser Pressure Holder Stainless Steel"
• The 32mm watch glass was found locally for under 3 dollars.
• The 20mm x 20mm extruded aluminum T-slot is 230mm long
• You will also need a 20mm to 25mm adapter that will glue into the bottom of the optical tube. (Also from EBAY "Adapter RMS Thread to 25mm M25 for Nikon Leica Microscope")

I still need to design a simple 5mm bright white LED light holder. But in the meantime you can use any source of stable light. The sun, a flashlight, or your cell phones camera light. 

That's all I got for now, need to get my car to the shop.

Apollo