@burcidi-- You don't have to do it that way. If you have an Indian or Southeast Asian grocery nearby, you can find both rice flour and lentil flour there.
Sometimes, they even carry dhokla flour which has both pre-mixed in a package. All you have to do is add hot water and any spices or yogurt in it that you want. But do this the night before and leave it to ferment just like the original recipe of dhokla.
As for steaming, if you don't have a steamer, you can put the batter into heat resistant molds and into a large pot with some water in it. It will steam in about 10-15 minutes on the stove like that. It's okay if the shape is different.