Been importing firearms for over 15 years now - I do all the paperwork myself, and believe me, it's just a tad more involved than bringing in a regular dutiable item! Having said that, it is not even remotely difficult.
If any dealer etc tells you Customs importation is difficult and overly time consuming, they are not being truthful to you to justify their usually exorbitant fee. There is NOTHING difficult about it - the most cumbersome task is to look up the correct code..all of about 30 secs work. Rest is just ticking boxes and filling them out. Most of my importing days were in the old hand written days, and all forms for a firearm import would take 20 minutes.
So, don't be lazy, do it yourself

The guys and gals at Brisbane Customs (located near the DFO shopping mall at the airport) are VERY amiable. Never had an issue yet - that's in excess of 500 military collectable firearms