Returning Hair to Natural Color After Dyeing?

I recently colored my naturally dark chocolate brown hair with medium ash brown permanent dye and I want to take it off, but I don't want to bleach it or color it another color because my natural hair color is impossible to find. Is there another way I can take it out without bleaching it or coloring it a different color? My school starts in August; how long would a solution take? Should I let it fade by washing my hair frequently and being in the sun? I'm really worried because the dye was permanent and it looks really bad on me. I really need to know plz contact me soon.