You can easily build a circuit for unipolar stepping
with ULN2003 or ULN2803, they are the same. I describe connections with ULN2003, you can make it with UL2803 in the same way, but look at the datasheet, you can drive 2 motors with 2803
You need 4 inputs (pins 2 - 5) and 4 outputs (pin 15 - 12) alternatively
5 VDC (VDD of control voltage) should be connected to pins 1,6,7,8
12 VDC (power supply for the motor) should connect to the centre wires of stepping
a 15V zener (depends on your motor). If you motor is 24 VDC or 12 VDC, it will work. the zener will be connected from power supply to pin 9
Others should be connect to 5VDC via a resistor (1K, I guess).
Good luck.
You may search for SMACK project on internet for understanding 2803.
They used 16C73 for 3 motors. One is used with 2003, two others are used with 2803.
In my circuit, I don't leave any pin free. You can pull it up to VDD or pull it down to GND, upto you, or you may leave unused pins free...
goodluck.