Broad question but we will leave aside 1941 in the Philippines and the Aleutians Campaign.
Typically the US Army wore a herringbone twill fatigue uniform in the SW Pacific. Usually they wore helmets without covers unlike the marines.
The only 28mm manufacturer that comes close are Perry Miniatures. In their US WW2 range there are a couple of packs in suitable uniforms. Fortunately the two packs are exactly what you require for a squad. Company support weapons, command etc you would need to source yourself but a little bit of work with a scalpel should convert the Parsons jackets in their plastic box into HBT shirts.
It’s a limited choice.