Actually, I had considered this - though I was not sure how well such a transformer would work. The easy thing to do would be to remove most of the windings from one side of a cheap 1:1 transformer. There are some on eBay at 800 turns, so removing 760 from one side would give the required ratio. But I'm not sure what that would do to the efficiency!Have you considered rewinding small audio transformers to get the turns ratio you want? It's not as difficult as it first appears. The tricky bit is getting the interleaved core laminations out without damaging anything, You know the original turns ratio, so count the turns as you take off the outer winding and rewind it using thinner wire, with the number of turns you need.
If you use three transformers with one connected across each phase, you can wire the secondaries in delta to a three phase Schottky bridge rectifier. That way, you will get the most available energy from the generator.
NOTE: When I was a project engineer, working for Hewlette Packard, the sign on my desk stated: "Miracles performed while you wait. The impossible takes a little longer." I never turned down a project. They were all successful and completed on time and within budget, So don't let people tell you your project is not possible, or a waste of time. Take their comments as a challenge, and prove them wrong.
Incidentally, I've heard that early radio control enthusiasts used to vary the capacitance of ceramic disk caps by grinding down one edge. Fiddling with the hardware at this level takes me back to the 1940s....