I second that, packages for posting wine bottles are a dime a dozen. See if one of them fits.
I have received sound advice for packing beers for post. To paraphrase it: Pack it well, pack it REALLY well. Once you've packed it well, walk to the door and throw it on the verandah. If the bottles don't break, you might be ok.
What I do is get one of those postal tubes, wrap the bottle in one turn of bubble wrap, with some bubble wrap at each end of the bottle and away she goes.
Ive sent heaps of PET bottled beer in those foam packs mentioned no worries around the country.I would trust glass bottles in them however from my locale the freight is just way too much hence the pet bottles only rule i follow.