Working out the 'gauge' can be tricky, as trying to match a gauge to the scale requirements doesn't always work. It's often best to try a piece next to the area being modelled. No idea where that would be visible on a Harrier though!
There are various types, some intended for armour models, and many are ordinary fine mesh as found in, for example, filters, as opposed to etched. There are metal versions, and a nylon type,known as 'Sylon', the latter again used in such things as fuel filters, tea strainers, seives etc.
These are normally vailable from Hannnant's and Model Hobbies in the UK, although everyday household objects, such as the tea strainer or seive mentioned, can often be a cheap source.