That’s dumb. All U.S. vaccine cards look identical and you’re not going to get some other design through.
You can still buy blank cards online.
Get a blank card.
Forge the information like on real ones that can be viewed online.
Be sure to use the name “Wile E Coyote” or “Donald J Trump.” If/when you are confronted just smile and say, “I know, I loved the Roadrunner cartoons so much I had my name legally changed. Beep Beep.” or “My parents name is Trump and they named me after the very successful real estate tycoon. Pretty cool, eh?”
They can’t ask for your ID unless you’re buying tobacco or alcohol so tell them you’re not. No worries.