I found the 2 ladies of Le Thanh Ton St ! - as recommended by
craftycathy in Ravelry's Asian Knitters forum. They're street peddlers alongside the famous Ben Thanh Market, Ho Chi Minh, just 10 mins from Caravelle Hotel where I stayed. Very convenient.
Gosh! it's amazing I lived to post this blog. I had no clue about crossing roads where (really) hundreds of motorbikes were coming towards you from every direction. Terrified, I would wait patiently at the curb for other tourists (esp bigger Westerners) then get myself strategically sandwiched in the middle while waiting for them to start the dash!! I did that at no less than 6 junctions.
The ladies were always packing up by the time I arrived there in the evenings, so never actually got to see all their wares. The quality of their yarn was OK and there's loads of cotton, all in lace or fingering weight though, nothing heavier. I didn't have time to look at wool which were all from China.
Here's the loot after 2 trips to their stalls...33 x 100 gms of 4 ply cotton sold loose and by weight.
Each is less than US$ 0.65!!! and I've no idea what to do with them yet. Bought 10 the first day, went back to the hotel to knit up a quick swatch, washed it for colour fastness and was quite impressed with the subtle sheen and softness. The next evening I went by taxi :) for another 23 balls.
All packed and ready to come home...