I assume by # you mean an actual number, and by actual number, I mean a floating-point number. As long as those two numbers are different, it should pick a new number each time. Assuming this is in an Update function, not Start or Awake. Which is what I'm guessing you did.

Replace InvokeRepeating in Start with Invoke in Update, putting your random value there.

Actually, you probably should use a 'timer'. Something like:

var timeBetween : float;
var lastTime = 0.0;

function Start()
{
  timeBetween = Random.value;
}

function Update()
{
  // check to see if random time has elapsed
  if ((Time.time - lastTime) < timeBetween)
  {
    // it has, get a new random time
    lastTime = Time.time;
    timeBetween = Random.Range (1.0, 2.0); // for example
    // spawn the item
    Spawn();
  }
}