It’s easy enough to get Euros from the Post Office, many Tesco stores have a foreign exchange desk (perhaps others, but Tesco is my regular store), or they can be ordered online from specialist dealers.

Mrs. Backwoodsperson travels widely in Europe with her job, she gets her Euros from the Post Office, not her bank (which, as it happens, is straight across the street from the Post Office).

No reason to rely on a bank branch.