I'll go into more detail later if needed, but since it's 1 AM I'll just do a bit of pseudocode

Basically you do an event in every monster group (make sure to copy it) that checks to see if you do an attack command, then:

<> Set variable [0001:EqWeapon] equal to hero's equipped weapon
<> Branch if [0001:EqWeapon] is equal to (weapon number)
...<> Set variable [0002:Knives] equal to number of knives in inventory
...<> Branch if [0002:Knives] is greater than zero
......<> Item Management: Remove one throwing knife
......<>
...:Else
......<> Set hero's weapon to nothing
......<>
..:End
:End
<>
(At this point the attack should continue normally)



Of course I suspect that this will not allow you to throw your last equipped knife. You may need to add another switch that is turned on at zero (instead of removing the knife right away), and another page to the event that checks for the hero's fight command AND the presence of the switch. That second page would remove the throwing knife weapon and turn off the switch, forcing the character to use his bare hands.