Welcome to 2022. Distributors in practice are low man on the totem pole when it comes to getting devices from manufacturers.
Large customers that have purchasing departments have delivery contracts they have prenegotiated long ago.
They are (mostly) getting what they ordered, not always. Everyone else is left wanting.
So I am speculating (I have no inside knowledge) that the Cyclone V family is not anywhere near EOL.
It us just massively supply constrained, with all newly produced devices going to existing volume customers with existing orders.
So what you would have to do is find some part that you can buy ALL the production quantity you need (or lock up in guaranteed orders) and then design around that part. Unfortunately I don't think you are going to find any part now that you can do that with.
Current industry pundits estimate that sometime in 2024 things should get back to 'normal'.