In vanilla Minecraft, there is no way (as far as I know,at least) to duplicate lava as easily as you can water, as the code for lava doesn't allow 2x2 pools of lava to regenerate themselves.
However, in Tekkit, one can use Equivalent Exchange to simply duplicate it. There may be easier ways with other mods, but you can generate buckets of it over and over as long as you have an Energy Condenser connected to an Energy Collector. Just put them beside each other, give the Collector some light (glowstone directly on top is preferable) and place one bucket of lava in the target slot of the condenser. There are way more efficient setups if you want to duplicate items, but the Equivalent Exchange wiki can help you out with those.