Look no further!
Real World Machine has a neat (albeit, not very fashionable) GRE score converter to make your grad school search easier. Just type in your potential grad school's GRE scores in the old scale and the scores get converted to the new scale instantly. The app also calculates percentiles, and has an alternate "new-to-old" converter, too.
Go ahead and try it! Until I can make a small program myself and upload it here, that's your best resource.
Happy studying and/or applying to grad schools!