Where to buy wash out hair dye?

i want to try dying my hair brown, but not permanently. i need to get that stuff that washes out in 10-15 washes... i've used it before to dye my hair red lol. but does anyone know what places carry those kind of hair dyes? i got the other from my friend, who got it from a friend, so i have no idea where they bough it. please be specific, dont just say "drug stores". thanks!