Where can I buy temporary highlights dye?

ok, so i have brown hair, and i want to dye the bottoms f my hair bonde, so it looks like its turning from brown to blonde. my mom told me that first i have to get those 18 or 30 wash hair dye thingies, which come off after 18 washes or something, so i see how it looks on me before i get it permanently. so, do any of you know like places that sell those 30 wash or 18 wash hair dyes? someplace like CVS or Target or something, or anywhere that yo know tat as it.