The most authorative versions can be found in the very famous Grimms Fairy Stories (Originally Children’s and Household Tales or in German Kinder und Hausmärchen) by the brothers Grimm. Jakob and Wilhelm Grimm collected and published transcriptions of oral German folk tales in the early 19th century, publishing their first collection in 1812. There are many versions and retellings available so try and get a complete and unabridged translation, here are a few examples of where it can be found, I have tried to link directly to the relevant web page on the site where possible.
Online Books-Full electronic copies of facsimiles of Grimm’s Fairy Stories can be found for free for example Internet Archive Rapunzel Rumpelstiltskin Google Books Rapunzel and Rumpelstiltskin
Online Bookshops-for example Amazon Abe Books
Library-For example North Yorkshire Libraries
Book shops-(you may have to order), you could try finding an independent local bookshop in your area