Dick! Hope you enjoy the forum. That is a great photo of your spotless tiger.
Della - if you do only have one immaculatum, then I agree that your idea to try crossing it with its spotted siblings in the hope of some additional spotless offspring is probably your next best bet. Definitely going to need some patience, though! I wish you all the best with it.
By the way, what is this 'normal' that you speak of?