Firstly, I pithed myself laffing at Jiff's carbon dating of Alex!
www.wwmeinc.com sells the models 1, 4 (in both white and khaki) and 5 for a most reasonable price of $39.95 USD ea and delivers (via Ogdensburg in my case) in two days. Our local cadet corps recently bought 10 in white for wear with patrol dress.
The supplier also stocks a "North Vietnam" cork helmet which is pea green and looks very similar to 3 but rounder at $19.95... it comes with an NVA hatbadge so may still be current issue to the Vietnamese Peoples' Army.
Cheers! Mike