Nobody carries charcoal canisters because you're not supposed to replace them, just the charcoal filter at the bottom.
As for dual snorkel air cleaners, I just don't understand why you'd expect these to be readily available as a new replacement part.
Just like the canister it was never intended to be replaced. You're just supposed to throw out the filter, not the whole assembly that contains it.
Those other things not being available are what happens when you own a 30 year old car. Supply dries up.
The way you constantly complain about not being able to get parts for your Regal, which has the best aftermarket support of all the G-body models, makes me think that you should just sell it and get something new. That way you can just stroll into your dealership and get whatever you want. Otherwise, it's time to learn how to use the junkyard like the rest of us...