U can just use twine from lowes. I got more than I needed for like a buck haha. Here's a link to my current scrog thread If u need help or got questions http://forum.grasscity.com/indoor-medical-marijuana-growing/1196843-herojuana-og-scrog.html
Two big things to look at when choosing string, you dont want something too fine like most fishing string since it can end up cutting into your plants. Also you dont want string that frays off too much like some twine can or ya may end up with small twine fibers in your buds. Think yo-yo string or mason string. EDIT: Didnt realize someone had revived a 3 year old post -.-