There are plenty of suppliers of 15mm UH-1's but the models are pretty expensive and some battles require quite a few helicopters. In the past I've used Matchbox and Hot Wheels vehicles in 15mm games. In this case I resorted to Corgi.
Corgi manufactures a police UH-1 that is the right scale and (roughly) the right variant. Roughly in this case meaning not the right model at all, but still recognizably a UH-1 at least. I picked up five on eBay for about six dollars a piece. Then I coated them with black gesso and set to work.
At this point I was hugely aided by the Vietnam Hueys page. This site, last updated in 2008, has some beautiful renders of machines that served during the war, in some cases accompanied by historical tidbits. It's a very nice resource.
The Corgis painted up very nicely. I used some colour photographs from Yahoo to pin down the dark green shade they were painted in. One thing I noticed in the historical photos is how the details seem to submerge in a mass of shadow. For that reason I tried to keep the drybrushed highlights to a minimum. Finally I applied some individual markings and matte painted the finished vehicles.
I'm happy with the results. They're not completely authentic for the period. On the other hand they were affordable and
as diecast models they are crisp and hefty. Next step are the M113s.