Find these lines in Game_Party:
@items[item_id] = [[item_number(item_id) + n, 0].max, 99].min
@weapons[weapon_id] = [[weapon_number(weapon_id) + n, 0].max, 99].min
@armors[armor_id] = [[armor_number(armor_id) + n, 0].max, 99].min
(180, 191, 202 if im not mistaken)
And change the number 99 to any limit you want.