In addition to the ///M Club Australia page that Prodigy has suggested, you could also try the two Facebook M2 groups - I've seen a few local (Australian) posts from folks selling stuff. The two groups that I'm part of are:
- BMW M2 Owners Group
- BMW F87 M2 Owners Club (I think that this is moderated by an Aussie?)
About half-ish of the posts in these groups are for products, so that'd suggest that you may get somewhere with selling your stuff.
Or just post in the AU section of this forum
I must admit that I've got stuff that I don't want (e.g. black grill surrounds) ... just never been that much bothered to sell it for the same reason you've identified
Cheers,