Organic or none organic
Organic.........Insecticide Soap Spray, but i don,t know if it will work as Thrips is not the easyest of pests to get rid of.
Mytex will do the job but you have to be carefull with it. Its used on Hens and pigeons to get rid of Red Spider Mite.
Before you use either you will have ti clear all the weeds etc around the leeks as this is where the hosts hide.