"...possible to make blanks for a .308?..." Yes and no. Most current military 7.62NATO blanks have a long crimped part where the bullet would be that allows feeding. That part can't be made with regular brass.
"...Do blanks simulate realistic recoil..." No. No bullet means no recoil. The gases are enough to operate a semi-auto rifle if you have a blank firing attachment(BFA). No BFA means no gases to cycle the action. That doesn't apply to a bolt action or revolvers though.
Blank firing movie guns either have a special blank barrel(semi-auto pistol like a Colt .45 require one) or a BFA in the barrel. If you know what one looks like and what a muzzle should look like, you can see the BFA on movie rifles. Especially M1 rifles. The distance from the front sight and the muzzle of an M1 is about a half inch. With the BFA on it's longer. Mind you, movie blanks are made to give a bigger flash than a live cartridge and the gun shot sound is added in editing.
Don't know about Australia(I'd be surprised if you could find 'em, given your laws. Semi-auto battle rifles being evil), but here in Canada, blanks appear occasionally at gun shows. In the U.S., they appear on some milsurp retailer's shelves. If you ever do find a box, make sure it doesn't say 'Grenade Blank'. They're much more powerful than a training blank. The crimp is much shorter than any bullet.
In any case, playing with blanks, of any kind, can be dangerous. They're not safe to play with. Brandon Lee, Bruce Lee's actor son, was killed with a blank out of a revolver.
