The only sleeveless guys in the Nam line were white if I'm not mistaken. Tanker was one of the ones I'm aware of, and the Tankers WERE available in a bagged 2-pack frm 21st's site (just called and they'd sell them to ya).
One was a tanker and one was a Platoon Leader I think, but both had just their flak vests on... No black guys though, and the arm joints are the awkward angled joints of old unfortunately.
The Viet Cong and NVA neither one have remvable headgear if I'm not mistaken. They were to just be very basic representations of generic enemies. They suck in that aspect.
Also, none of these figures are especially cheap anymore I don't believe. Nam stuff sorta took off after the line died at TRU unfortunately. May wanna check around Ebay though, as you never know what you'll get.
I know there's guys clamring for it though. I never bought into the Nam line myself.
Sorry for the lack of real help there.
The only thing for Asian heads I can suggest are the Bespin Guard and Y-Wing Pilot from the 3-pack. And I'm sure you're tired of using those 2 probably and that's why you asked.