After 9 million plus tech points I gave up on that tribe and it's missing feather.
Not having any better luck with current group. Can tell you an approach I tried hoping for better results...leaving the cave rubble & debris until other three categories collected has not helped!

After 10+ tribes, I've decided it's just dumb luck. I've completed the collections in 4 or 5 villages without even trying. One especially lucky village had all of the feathers, all the shells and all but one rare coral before the first babe-in-arms was 5 years old. As soon as I started clearing the rubble, I had pieces appear every few minutes and was done all collections before I started the statue or sewing hut.

Other tribes I have run the kids ragged collecting, used the chief to help point out rares, and I still can't get that one last feather or shell.

I am on my fourteenth completed game and have got all the collectibles in all games except for a tablet piece, or two, in each and every game. I agree this can be hugely frustrating, it's one of the low points of the game IMHO. Apart from that I love it. Does anyone have a spoiler for how to get the tablet pieces quicker? I have found that if I click on the collectibles on the collectibles page when I don't get one for a while, one turns up shortly afterwards, (perhaps a coincidence) but not so with the elusive tablet pieces.

Success! After "only" 442 Isolan years, that last, coveted uncommon tile piece appeared like magic while I was stoking the fire. The kicker? Still have not had any triplets

i give up too
one village i have all the collectibles,
another village i have all the awards
but i cant get one COMPLETE village

I was curious so my last game I decided to watch the rubble clearing exclusively, and note down when I got the tablet pieces. After waiting until 5% for my first piece I got one at 6%,10%,11%,18%,18%,21% and 27%. I am now at 68% and haven't had one since!! Not only is it frustrating, it is REALLY boring! I do fly over the map occassionally to check on everyone and to grab collectibles and mushrooms. I have to say this is the worst part of this game. The rest I love!!

Can anyone tell me what it is that the tribal chief does to help find rare collectibles and how to get him to do it?

If you click on the "?" next to Leadership tech on the Tech screen, you will see a description of all of the chief's special abilities, which can be performed only once every 24 real hours (according to your computer's system clock).

There is a good discussion of how it all works in this thread.

Thank you for the quick response.

I have completed all collections (excepting Keys, as they are mandatory to completing game). It did take a while for final Rare Shell to show up though. It'll happen to y'all as well. I was about to give up as well a couple of times.