Very unusual not to have a restrictor, it creates the proper backpressure so water gets fed through the membrane. I wonder if it already comes with one installed. Some restrictors are inside of the quarter inch black poly tube. It should be right at the connection where the black tube comes out of the ro membrane canister. It will look like this:
http://www.marinedepot.com/Flow_Rest...RORAFR-vi.html
And is pushed into the black tube so only the shoulder is sticking out. Mine is coloured black and its hard to see unless youknow its there.