When you give blood at the Red Cross you can register and schedule an appointment online by opening an account.
https://www.redcrossblood.org/
After you give blood they will post your results to your account a couple of weeks later.
It’s free. It just costs you your blood.
And that is a screen shot of the result from my account.
Just a suggestion but if I were you, I would 'print' that out and have it ready in case you are challenged about not getting the 'jab'. There's no reason to insist on it or refuse 'services' if you've had C19, have antibodies and have proof of it.