I picked up a nice bunch of Hong Kong used in China and Japan. I'll add a few of the nicer strikes, but I would like to see yours, too. Gibbons lists these with separate catalogue numbers, based on the usage and the underlying stamp.
A blue barred oval F1, Foochow:
Quite certain there should not be a straight edge, but I wasn't going to pass up the cancel.
A 10c red used in Shanghai:
A pair of 2c, one Shanghai, one Canton:
Another Shanghai, this time on a 5c:
Another Canton, on a 2c:
Hankow, on a 20c overprint:
Leaving China for Japan, a blue barred Y1 from Yokohama on a 2c:
Leaving Victoria for her son, Edward VII, a Wei Hai Wei cancel from Liu Kung Tau:
Last for now, and probably the least CV according to Gibbons, but one of my favorites, an Amoy strike on a KGV 30c:
With respect, I have trouble with your thread title, not that I have a solution either, but here's my thoughts.
In 1864 it was compulsory to use Hong Kong stamps from the Treaty Ports. That's fine, your thread title encompasses that. However in time, that rule became lax, and the Treaty Ports began to use their own Postmark Cancellers. Your thread title would not encourage the discipline to a broader range of examples. eg Szeming (Amoy) treaty port cancellation on a Chinese stamp, the "B2" canceller et al.
Stanley Gibbons lump those under "British Post Offices in China", I don't care for that either.
Gibbons quotes a Treatise "Hong Kong and the Treaty Ports of China and Japan" by F W Webb
That would seem to me, to be the best, up till now, I have had all mine under China / Treaty Ports / Amoy, (etc & etc 16 ports)
It doesn't worry me here, I save all images to my own Hirearchy, but I thought it worth a mention for polite discourse.
PS: The Foochow and Yokohama are beauties, not seen those before.