How do you CS past laning phase?

I started ranked very late last season and was slowly but steadily climbing my way from bronze to gold. The season ended before I could reach it though, and I ended the season at silver 2. I consider myself a low tier gold player (gold 5 - gold 4), and I base that on how well I perform against both higher and lower elo players.

Anyways, I've lost pretty much any motivation I may have had to do ranked this season and I mostly just play normals now. I can CS just fine in laning phase - I average roughly 8 - 10 CS per minute. After about 12 minutes in normal games (and lower elo games) it seems like the game just becomes team deathmatch, where everyone is looking to start teamfights whenever and wherever possible. Team fights start breaking out all over the map constantly and for no apparent reason. Everyones fighting fights that don't need to be fought, and after this point my CS dies and goes to hell. If i don't show up for those team fights then my team more often than not tries to fight a 4v5 and then blames me for being somewhere else farming when they lose. And during those short moments between teamfights, everyone is rushing to lanes to kill every minion they can before someone else on their team beats them to it. This isn't every single game, but it feels like it's the majority of them.

How am I supposed to keep up a decent CS number whenever I'm expected to be everywhere, and when nothing big is happening everyone else is racing to grab all the CS?