It was so predictable that fake vaccination cards would pop up in the black market.
See Prohibition.
People will find a way to do what they want to do.
Making, selling, and possessing them is a violation of Federal law against unauthorized use of a Federal agency’s seal: https://www.ic3.gov/Media/Y2021/PSA210330
Sure, some people will choose to lie and commit Federal crimes to avoid a private business’ requirements, but that’s the risk being taken. But hey, if sticking it to the bar owner is worth risking 5 years in prison (https://www.law.cornell.edu/uscode/text/18/1017), then by all means.