Easy. Your first stop should be your Japanese equiv. to "Toys R Us" store.
Many toy companies have figured how to do it for a few yen, only with a small motor and cams, why can't you then?
Hint, small motor, gear reduction to drive cams that position legs, robot is always wearing big snow shoes, "A walking robot walks best walks always with small steps!". Big Feet balance a low center of gravity to not tip over.
Once you got that right, you can move on to perfect your own Asimo.
A control theory fanatic like Chairman Mao once said, "Two Steps Forward, One Step Backward." His idea of progress..maybe you can start dancing with that idea.