To take full advantage of the charger you will need a 55 amp 24v supply or a 100 amp 12v supply.
To charge 2 6s batteries at 1.3 amps, you will need a 65 watt power supply. So either a 6 amp 12v supply or a 3 amp 24v supply.
Your cheapest option is an old PC power supply. they are cheap and most can deliver 10-15 amps (120-180 watts) at 12 volts.
There are also pretty common Chinese units that can output some power. Here's one on
Amazon, but you can find them all over the place. The 24v/15a model will do 360 watts, which will charge a 6s at around 16 amps.