i read somewhere that they won't spawn if you have a bunch of trees/flowers/items in your town. is this also true? because i have a ton of flowers and trees and i don't want that to be preventing them from appearing
Save and continue will be your friend here. They reset bug/fish spawns. So just wander around town around your open areas (they don't spawn on top of patterns or flowers, it seems) and if they aren't there, save and continue. Repeat this until you find them. This is what worked for me and I literally found it easily (I had lots of patterns and flowers too so I only had to check the very few open spaces in my town). Not sure what time but it was after 7pm for sure.
I'm really struggling with this right now. I've got a few clear spaces in Fujimori specifically so I can catch these suckers, but they don't seem to want to come visit me. :'(
it happened to me twice in Town Kenma, but i got stung both times. I nearly caught the scorpion though