Unfortunately, in plastic, there are none. You can use some of the older Tamiya ones, but they are generally bad.
In resin, there is one set by Valkyrie.
These also include the more modern DH-132 CVC helmets which were issue from 1973 to present (with a few updates, but they look pretty much the same).
They also offer a '80s-'90s version of a very similar set w/just the DH-132 CVC helmets.
If you can find them, Bravo 6 did a very nice set of 8 '60s-'70s T56-6 “Bone Dome” CVC helmets with PE boom mikes. They can be used to update the older Tamiya sets or to help backdate any figure.
If you want some grunts on the ground around them, there are a couple of options, sort of.
If you take the new Tamiya Infantry Scout set (35379) and swap helmets for camo covered ones, weapons for M14s, and newer boots, you have early '60s infantry in basically OG-107 Fatigues and field jackets. If you use M16s, ALICE ammo pouches, and H-back web gear (available from Bravo-6), you have late '60s through early '80s infantry in the same. They won’t be prefect for the time, but close enough.
The same can be done using MiniArt’s U.S. Soldiers Rainwear set (35245). This includes 3 figures in ponchos and two in raincoats. The ponchos are pretty much universal and still pretty current. I’m not sure when the raincoats went out of use. By changing helmets, boots, and weapons, you can represent '60 through modern troops wearing the ponchos.
That is what I plan to do with them any ways. We’ll see how they turn out.