1970 Cuda 440-6 ECS - Correct California Gas Cap Needed

[V Code Dave]

My wife and I own a 1970 'Cuda 440-6. Matching numbers car that we purchased in 1989. This is a California emissions car. It is supposed to have a vented gas cap. I have been told that it is a specific gas cap just for California emissions equipped cars, not a standard, vented version.  I have checked with all the usual places and cannot find a non-vented  gas cap that is designated specifically for California ECS cars only. Am I searching for a unicorn that doesn't exist or can the non-vented, typical E-body cap work?
I appreciate any advice. Respectfully, Dave

[floorit426]

Here is a pic of mine. This is original to the car. I have a few extra caps, but I'm pretty sure they are all vented. I'll check and see. That is a very nice looking car, by the way.