Transfer items between two of the RuneScape accounts

Jagex does not seem to release information in general about the trade volume of every item in the game, but as Warface pointed out, Jagex releases some of the statistics about the top 100 most traded items for a given time period. This shows for a time period of 7, 30, 90, or 180 days a few trade volume statistics for the 100 most traded items during that period of time.

The only way to fight with dual-wielded weapons is by equipping a normal one-hand weapon in the main weapon slot and an "offhand" weapon in the offhand/shield slot. These offhand weapons are separate items from the regular weapons, each corresponding to an existing one-hand weapon. Each offhand weapon can be obtained in the same way as its corresponding regular weapon.

Almost every one-hand weapon has a corresponding offhand weapon. A notable exception is the Abyssal Whip, which apparently had animation issues. One other oddity is that dragon claws, previously two-hand weapons, are now separately obtainable as claw and off-hand claw.

As far as I can tell, the only real difference that comes from the extra weapon is the extra DPS.

Almost all of this information comes from this reddit thread I posted.