Stepper Motor Sources

Some of the sources are suplus sources and inventory varies
Not all motors are suitable for CNC type machines

Oriental Motor (Vexta)
Automation Direct
Keling Inc
MPJA
All Electronics
EIO
Electonic Goldmine
Electronics Surplus
Surplus Center
Anaheimautomation
Interinar
Xylotex
Hobbycnc
Home Shop CNC
Click Automation
JAMECO Good prices on L297 and L298 chips

Machine Mechanicals

ENCO
McMaster Carr
MSC
VXB Linear Bearings and shaftng

Electronics 

Mouser No minimum
Digikey

Transformers

MPJA Highly recommend the 24V 10A and 24V 4A transformers
Antek Nice Toroidal transformers for stepper and servo supplies