I do have a bicycle-generator. Built it myself. I'd be happy to share all my design work on it. I used a car alternator, but those are designed electrically for cars - I had to completely rebuild the voltage regulator electronics to make it more efficient and able to operate at lower speed.
Human power is a novelty, but the awkward truth is that humans are just pathetically weak creatures. There are certain niches when you want a little power but without the shelf life and maintenance concerns of chemical cells, like plunger detonators and phone magnetos, or wind-up radios. A human-powered generator might even be good for a really remote little shack, as it can provide enough power to operate lights and a radio in emergencies without being dependent upon the weather. But energy-harvesting walkways? That's just silly.
Let's say a human weighs about 800N. Actually, this is probably for the American market, so call it 1000N. A maximum comfortable 'sinkage' in stepping is about 0.5cm. That's 1000*0.005 = 5J per step. At a stepping rate of 2Hz for a brisk walk that's an absolute upper limit of 10W... or about the same as one tiny little solar panel that will be a fraction of the cost. That's assuming every component is at 100% efficiency, of course, while in practice that's just not going to happen. You'll be lucky to get 10% of that ideal figure.