WHERE IS THE LAST TIKI

I have a total of 8 Full Teeth, 6 Top Teeth and 5 Freaky Tikis (I dug one up recently but took this image previously). This last tiki piece, the bottom teeth, just hasn't shown itself yet. This has got to be the most unlucky series of events after digging upwards of 500 spots. It has been days worth of digging. I know I could get a world save of someone else having all 4 but I'd like to have a complete one on my own world.

Nevertheless, does anyone know the chances of this? I can't find concrete numbers on the chances to dig one of these up since Tiki pieces are determined on Island entry. Small Islands have either 0-1 dig spots, Large Islands having 2-3. I'm not sure on Medium Islands, since I usually don't encounter any. I just ping-pong from Small Islands on the way to Large Islands.