an FAC form can be picked up at your local RFD or police station.

an airgun that is over 12ftlbs MUST be registered as an FAC gun (firearm)

you are allocated what is called 'slots' these are the amount of guns you can apply for at any given time (there is no limit to how many you can apply for/own if you have 'good reason')

a moderator as we burners call em (silencer) uses 1 slot

so for example, an FAC airgun and a moderator = 2 slots

you must have 2 referees who can vouch for your character and competence
also required is passport photos (all this info is on the application form)

HTH
Deano