In the meantime, you can start a thread in How's It Growing? | UBC Botanical Garden Forums. It says "A casual forum to keep in touch and share photos and stories of your gardens." We've been using it to post anything that's growing anywhere that doesn't fit somewhere else. It definitely has postings of things seen but not grown by the poster. If you're not looking for discussion on the tree, a thread that fits could be https://forums.botanicalgarden.ubc.ca/threads/out-and-about.97971/. But if you're hoping for on-going discussion, a separate thread would be better. I'll second the request for a Trees forum. You'd want the name to be something that isn't "Other Trees". Maybe Trees works.