I just ordered a couple of gears from the above surplus supplier. It includes a small one with 1/8" bore which should fit my small 6V 10RPM motor which I might use for motorizing the RA manual knob of my TG-SP II, and it also includes another set of two. For that set, they have 1/4" bore so that one of them could fit the RA manual knob of my TG-SP II, thus working with the first gear as a pair. The second one of the set would be used on a bigger 12V 5RPM motor which I will be using it for motorizing the DEC of my TG-SP II.
Both motors were tested to work with the motor controller box which I've finished yesterday. Adding a ST4 style autoguider jack for this controller box would require a simple pull-up resistor so it's very simple indeed. However, I will not go this step until I've the chance to get a guiding adapter like Shoestring GPUSB or a guiding camera, but then I believe that I won't go this step in short term since I will not go for longer than 200mm.
Someone offered to buy my 9mm Meade reticle, so I will not be doing manual guiding via eyepiece afterward, instead, I will guide manually via my DMK with a CCTV lens by looking at the video output rather than the eyepiece.