Probably one of the most iconic and fan-boyed-after camouflage pattern families is the Tiger Stripe one. I have found a source to get very nice reproductions of the locally made ARVN pattern, sized in U.S. Sizes that was used by U.S. Troops during the Vietnam War. These are made out of 100% cotton twill like the originals, and are cut in the same pattern with the "cigarette" pocket on the left sleeve. The modern "tiger stripe" you can buy isn't historically accurate, nor does it look quite as cool as these.
The pattern used in this particular uniform is one of the most common, and is referred to as just the "ARVN Dense" pattern by most. This is the most commonly seen pattern among U.S. and ARVN forces, which makes it perfect for your impression.
Even though these are in U.S. sizes, like originals, they are what I would call the "Slim fit" cut. If you want a more loose fitting shirt, order a size up. For those of us fellas with large bellies, you also may want to go a size up.
NOTE: These are a made-to-order item. This means that after you order, please allow for 3-4 weeks before it arrives to you. If it will be longer, I will let you know. Trust me, it's worth the wait as these correct uniforms are VERY hard to find and highly sought after.