low gear ratios (25:1)

I am designing a low speed(6mph) electric vehicle that will be used to transport loadings of about 400lb and will have total weight(loaded) of 1400lb. I will be using an electric motor with a 19 tooth spline from a golf cart and calculated I need a gear ratio of 25:1. However no rearend assemblies I can find are anywhere near this ratio. Does anyone know of a solution of how I can get such ratios or if such ratios exist? I know you can get large/low gear ratios with worm gear sets however I cannot seem to find any worm gear differentials.