Heresy of John the Baptist

I've heard of a heresy that believes John was the "REAL" messiah and Jesus usurped his authority ....Anybody know more about it ?

I believe " alternate Belief" would be a more appropriate term. Yes there were/are those that believed John was the true Messiah. There were/are
those that believe John and Jesus were both messiahs. The Aaronic Messiah/
John and the Davidic Messiah/ Jesus. one civil, one religious, the columns Boaz and Joachim.

Where can I find out more on this ?

There are several books that talk about it. The Second Messiah ( i think thats
the title) by Henry Lincoln is one . The Hiram Key is another, they make some
very large leaps in this one but the bibliography is useful. that is a start and always check the authors sources and biblios sometimes the references are better than the book.