I lost the front sight to my Gamo Hunter 440 a while ago. I presume you talking about the little black and red fibre optic thingy. Your gunshop can get a spare from Nicolas Yale the importers. It's about 80 bucks for a new one.
Too expensive. I bought one for less than a quarter of that price from Jason once, for my Shadow. Importer offered one for free. Just go and fetch it, you will use less petrol than R80-00. If you are going to use a scope you don't need it, it will most probably be in your way anyhow.