"Why are Sinnoh Stones so hard to come by?"

#PokemonGO: I've been playing PoGo for awhile now and been consistently getting the weekly pokestops rewards even before they introduced gen 4 into the game and so far, I've only gotten one stone. I've tried battling friends (my gf got one from the battle), spinning new pokestops, and still getting the weekly rewards and I still can't get them.I have so many pokemon that require it to evolve (including two shinies) and it just bothers me at the rarity of the stone yet I can get more metal coats than I know what to do with. I'm not a hardcore player but I play enough to where I should have received another by now. Am I missing something? Is there some secret to finding them? via /r/pokemongo https://ift.tt/2YOX4Nh