Too many magic rings and trinkets

I am a DM, and I have two player’s who love +1 Ac Rings, or any kind of ring or trinket to help with AC. Every bit of gold or other item of any value they use it to trade for it.

I try not to be mean about saying “hey, you can’t have all these rings on” but they say back “nowhere does it say how many I can have. I have ten fingers for a reason.”

Is there anywhere it says how many rings/trinkets you can have? And how can I stop the purchasing and finding of these rings without completely looking like the bad guy by controlling this?