Can you get your hands on a 40-gallon stainless drum, some perforated pans, some #10 Bunn coffee filters, and a couple of hot water heating elements?
I can steam 20 lbs of rice at a time, I usually do three or four batches in an evening to keep the sake pipeline full at my current pilot-batch level. I too am going to have to learn how to scale up (by a factor of 8) when I start doing full-size batches at my little saké and beer brewery.
(That smiley up there was supposed to be an 8 but I think I like the factor-of-smiley better.)
Here's how I am currently steaming rice:
The smaller white bucket holds just under 20 lbs of dry rice. Convenient for measuring.
I drain the water and distribute the rice among the pans. The coffee filters are there to keep the rice from falling through the holes in the pans. Also it makes cleaning the pans easier. Some rice sticks to the paper though.
The drum holds four pans. I drilled a couple of holes and used hot water heating elements (with weldless fittings) as my heat source.
A piece of foam on top with a weight keeps the steam in but doesn't turn into a bomb or anything.
... and cool the rice on a huge piece of polished granite that was left by the neighboring shop when they moved out!