Hi Markus, there's a group in Mandurah, their information page is here: http://www.bcna.org.au/membergroup/group/mandurah-breast-cancer-support-group. ; They only give an email address to contact, but give that a go.
If you want to do a search, this is the link for the page to search for face-to-face groups. Just put your postcode in and see what comes up: http://www.bcna.org.au/membergroup/search.
Hope that helps, there might also be some online members who are in your area, but I'm sure they'll jump in and say so if they are.
Di