Hi, You should have one at the end of every Sprint. Be warned however in some - very large - organisations you might actually have ..2 one with your PO and stakeholders and one with the "big brass" meaning some senior managers who might want to have a look on the outcome.
I would recommend (if it is happening) that the 'big brass' come to the regular sprint review meeting. If they say they don't have time, then it obviously isn't important enough to them. There should be complete transparency and having 2 different sprint reviews goes against this, as what is discussed in one may not be covered in the other and you have many people missing out on key discussions.