For your information, 'There are so many Johns' in England can mean there are a lot of male clients of prostitutes which could give your text a very different meaning!

Sorry, @Shirleen @Paul, I made a mistake. And thanks @Paul for your picking out my mistake. and your explanation.

Shawn, your example sentence has a very different meaning to what Shirleen was trying to say. It's also not a correct sentence. Shirleen, to answer your question, yes, you can say 'There are so many Johns.' It has to be plural, you cannot say 'There are so many John.' You can however say 'there are so many people called John/there are so many men called John.'

A good question. I think it maybe a language habitat. 'John' is not a noun. I don't know if we can put 'John' in this position. Maybe ‘There are so many names for/after 'John'’ is much better.

Yes, you would add an 's' : 'There are so many Johns.'