I'm getting some coilover for my vw polo 6n but I've been looking and I can't find any for a petrol, I can find them for a diesel and I'm just wondering if they would still fit a petrol even though there for a diesel?

Your profile picture shows a 6n2 are you sure its a 6n?

The standard struts are the same physical size/shape just the spring rate & damper are a stiffer spec for the oil burners than petrol engine cars due the heavier engine, so if the coilovers are for a 6N then they will fit, in all the adverts I've seen they don't specify engine it's just for a specific year range/chassis ie 6N