Where is Breredon please ?

[Raynor]

According to the Maps of Lotr Chapter of the Hammond and Scull "Reader Companion":

Tolkien expanded the geography of this part of the Shire in his Preface to The Adventures of Tom Bombadil and Other Verses from the REd Book (1962), in regard to his poem Bombadil goes boating:
...

Hope that helps; I am quoting from the Companion, since my version of the Adventures doesn't have this bit of info.