Where can I buy a face mask?

Is it possible to buy a face mask to wear when I am spraying insecticides? Even on calm days spray drift can blow back and breathing in some of the vapour is unavoidable, especially when spraying tall things like raspberries.

There’s a bit of a paradox here. You are concerned about particles of dilute pesticide landing on your skin, but happy to spray your raspberries which will be eaten later. If a droplet or two of insecticide on the skin bothers you, aren’t you concerned about residues in the fruits?
The range of pesticides available to home gardeners is extremely limited. All available products are safe, having been rigorously tested over long periods of time. Any spillages on skin can be washed off and you can protect your breathing with a simple, disposable face mask.
You can buy face shields as well as filtered breathing equipment. Try www.jsp.co.uk or consult an agricultural pesticides specialist. You can also use lightweight waterproof coats and Neoprene gauntlet gloves, to ensure skin protection.
It’s not a bad idea to keep pesticide use to an absolute minimum anyway. Avoid using any chemicals that worry you on food crops.