where can i buy 20 vol.?

i had to go with my mom to the hair stylist today and i sat there watching her get her hair highlighted. i had asked the stylist what i should use to bleach the tips of my hair and she said 20 vol. considering it only takes less then 20min for my mom to have bleached hair that is what she suggested. she said she could do a strand test on me so i let her and it bleached into a nice color after less then 10 min. i have seen only 30 vol. i have been lookin up some sites but just cant find any. does neone know of websites or stores where i could get a 20 vol bleach kit???