I don't expect to see too many responses, but please surprise me. This one showed up today. The Centenary of Shepparton, Blossom Town of Victoria, Australia. I don't know how far this pack horse trip went, and the cancel is undecipherable, but probably 28 Oct 1938. There are some signatures at the bottom, possibly by one or two of the riders. (Nothing on the back.)
I don't know what is crossed out around the words "Pack Horse". I saw another copy on eBay
and it has the same blocks, but no signatures. Enjoy.