Any higher gear ratio will be too high to use the OD, and no, there are not any other sources for the 3.55 gears. They're all made by a single supplier in China, I believe. Mothertrucker has a better price than the other vendors for the same gearset since he made a volume purchase from the manufacturer. A better price won't make the gears work any better with an overdrive transmission. The engine doesn't have enough torque to pull the higher gear in OD.
Jerry