I have one pair of high-quality Vexta PK245-01BA steppers [200 steps/rev., unipolar, 6-wire, 4v., 1.2amp] left over from Bartelizing my 17.5" Dob (now fully GoTo / tracking capable). I found these to be perfect due to their good torque (44 oz-in) and yet small size/square form-factor. They microstep smoothly over a broad range of input values and handle 12v. quite well. If interested I can probably dig up more specifications and pixs. Some specs can be accessed on-line (contact me for info).
The bottom pix is one of these Vexta's driving a nylon threaded rod that mates with my elevation sector (epoxy gear on its edge - not shown).
I will sell these for $15 each + shipping (normally used in pairs). Thanks, Nils.