JCT1990

Hey guys... Ive got an 06 xlt and I live in the great salty north east.. I dont know if this is a common thing or I'm just .. lucky.. but my trucks bed "rails".. "Supports" whatever you want to call them, are rotted out.. as in they arent there anymore.. so my bed is basically useless right now unless I want to dent the hell out of it. What exactly are these called.. and where can I get new ones.. or what else can I use to replace them?