Here's a site with a number of DIY stepper drivers.
These all requires a
step and
direction input.
You'll still need to provide a suitable source of correctly timed pulses to get your correct tracking speeds.
If you're only after a low voltage, low current device, you might consider an
EasyStepper. Ready made and less than $20.
[You can also get the EasyStepper from
Ocean Controls in Melbourne]