Yeah, the NIF database is your best bet. Their weapons are actually a little off though at times. It also a good idea to check out the Web Resources page at the NIF Database.
A little? I have the Executor's weapons outfit memorized by heart. 250 Heavy Turbolaser Batteries, 250 Turbolaser Batteries, 250 Heavy Ion Cannons, 250 Concussion Missile Launchers.
And what does this site list?
1,000 Heavy Turbolaser Batteries 1,000 Turbolaser Batteries 1,000 Proton Torpedo Launchers 1,000 Ion Cannons.
Everything else, except speed, looks fine. But hot damn, that armament is way off.
As for finding sources, trying inserting various ship class names into search and going from there. Usually I'll try Intrepid class Carrier or Mediator class cruiser for more up to date canon references.