Its considered toxic if ingested and I dont think you can buy it in the UK. Used mainly to control mosquitoes? Maybe used in head lice treatment though?

Malathion is an organo-phosphate and quite rightly has been banned because of its potential toxic effects.
When it's absorbed into the human body it is metabolised into malaoxon which is much more toxic.
Why do want to get hold of this awful product? Use a natural predator for your problems if possible or other organic techniques.