Your problem was my problem some month ago. No, most active units - if not all - had switched to ERTL + Fritz helmet by 1986. Exceptions would have been found in ANG units, which is why I bought Vietnam era troops, too. I completely went for 20mm though. In 28mm the possibilities for US Cold War forces are meager, vehicles are very rare for all nations and extremely expensive.
Hobby Armor Depot has very nice things, SciFi and 20th century: http://hobbyarmordepot.homestead.com/catalog.html
But for 20mm (and 1/72) the prices are half of what you pay for 28mm.