You could just look for some misc transformers snd try them 6v, 12v, 18v, 24v until you get to the minimum size that works. Look for parts off old clock-radios, printers, etc.
Or, find a friend with a DC power supply and connect through the bridge rectifier (it doesn't care if you supply AC or DC and doesn't care about polarity - the bridge will make it right for you. Look at the heat sink (out +/- are labelled, just put the DC into the opposite two terminals - typically labelled ~ but not in your case). Start at 5v and work your way up 1V at a time until the thing comes on.