Once I stopped purposefully looking for cicada shells, I started finding them every now and then while roaming around doing other things. I've found 5 so far - one went to the museum, 3 went to Flick for a model, and I have 1 left over. I might order another model if I run across 2 more.
I've only found 2 walking sticks, but one of those was just by chance as well. It helps to have plenty of trees spread out over most/all parts of your island, of course.
In other news, I had a villager ask to move out so yesterday I had an actual empty plot on my island for the first time in a long time. Since I have all of the amiibo cards for the villagers I want, I decided to try the NMT method to see if I could run across any of the new villagers that don't have amiibos (specifically Sherb or Dom). 35 NMT later with not one desirable resident in sight, I gave up and just used the Lucky amiibo I'd been holding onto for quite some time. Welcome, Lucky! You get to stay until at least Halloween.