Can you give me some examples where "ain't" is used in place of "have not".
According to Oxford Dictionary, ain't=am not,is not,are not,has not,have not.
It replaces have not when have not is an auxiliary verb, not when it's a a conjugation of to have:
"I have been racking my brain, but I ain't been able to come up with a good example."
"I have done a lot of bad things, but I ain't hit a man with glasses or stolen from a baby."
A very common combination is "ain't got" meaning have not got (or, briefly, don't have) A google search will reveal that "ain't got" turns up in lyrics all the time:
While we generally avoid the double negative in English, you can see in these examples that "ain't" often bucks that trend and pairs up with a second negation (nobody, no home, no)
Note: This would not be considered standard written English. In some parts of the U.S., it would be fairly common to hear it in spoken English (e.g. Texas), but from a second-language speaker, it would sound strange, unless you are extremely fluent.