Buying birds in HCMC

get a Vietnamese friend to take you down to the parks / coffee shops where people display their birds on the weekends in the mornings. You'll definitely find someone through the meet up group with some birds to sell

Vietnamese men keep birds as a competitive hobby.  You can see them traveling with caged birds shrouded and strapped to the back of their motorbikes.  Generally they are going to specialty cafe's that serve as gathering places.  You can recognize them by the bird pictures on the signage.  I never went to one having been to enough "chicken" fights in Hawaii, but the wife tells me that they compete by placing cages next to each other so that the birds will compete by song and they will occasionally put two birds in to one cage for direct combat.  I expect that they compete with male birds but someone must be keeping lines of breeding females in the same way lines are maintained for fighting roosters.

Lê Hồng Phong in D10 is a pet store street. north of Nguyễn Trãi. Sad dogs, cats in cages, and should be birds too. Mostly 'inside' shops.

There are also birds sold in this alley, Tân Hưng, in D5 here .  Definitely were budgies and song birds among the roosters and doves. Don't know about cages though.

Coffee Shop - Ngoc Nga Canary in Binh Thanh district.
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Went there a few days ago.
A small shop, their prime business is breeding and selling mostly exotic birds. They also sell bird cages, bird feed, feeders and all other accessories one may wish to have to keep birds as pet.
You can take a 15k coffee and sit there observing the birds.

Birds on display included Canaries, Budgies, Indian Parrots, Lorikeets, Finches, Lovebirds, Macaws, one Myna, several Cockatoos and a lone Drongo. Some of these birds looked in good shape.

I saw a box full of chicks (prolly budgies). They were being hand-fed. The way the owners were handling those tiny birds was, IMO, awful.

Worth checking it out though!