Check out Underarmor for good synthetic undergarments. I like Columbia Sportswear or similar cargo style pants and long sleeve shirts in synthetic as well for their breatability and protection. Look for pants with zip off legs and shirts with lots of venting. Also get a decent hat that will shield your face and neck. I have a good wardrobe of these type of clothes and wear them as business casual at work and around town. They worked much better than cotton clothing while I was in Baghdad, and were a lot more comfortable. The colors and styles are practical and don't have that "tactical" look you are trying to avoid.

The good news is all of the stores you mention carry these type of clothes. The bad news is they are going to be a little more expensive than their cotton equivalents, or regular dress shirts and slacks would be. If you opt for more conventional clothing, I would still recommend synthetics in a hot environment, but look for lighter weight fabrics.

Check out outlet stores if you can find them, you might find some really good deals.