After 5-7 visits, I FINALLY SAW WHITESHADOW WITH MY OWN TWO EYES!
Now I shall not so patiently wait for his memento. 😤
PS: Whiteshadow and Tubbs are the only cats that do not get kicked off when you change the remodels. However, they can get kicked off when you change the furniture or refill the food (ditto for Tubbs). Thanks to the awesome people over at the Neko Atsume subreddit for providing these insights! 😊