Here are a few transformers I found. Be careful of the DC volt output, you will burn up the drive if you go higher than recommended. To calculate the approximate DC volt from a transformer multiply AC volts X 1.4 ex: 28vac X 1.4= 39vdc Using a good capacitor or two to help filter it.

28vac, 12amp, $35
http://www.electronicsurplus.com/com...6-6-132859.htm

28vac, 8amp, $25
http://www.electronicsurplus.com/com...-56-4-8016.htm

44vac, 13amp, $25 WARNING: this is about 62vDC !!
http://www.electronicsurplus.com/com...942b-39987.htm