A couple of days ago I got one of the missing beetles. Then I tried switching the 1/2 speed to see if the ones I was still missing would show up (as suggested above.) But that didn't seem to help any so I went back to normal speed.

This evening I was on the phone with a friend, so I was watching my village and villagers keeping an eye for the missing collectibles. To my pleasant surprise I got the last missing beetle and a few minutes later the last missing pebble! The collections in that game is now complete!

So my advise is again: just be patient!