I think you mean Lvl IIIA armor. Lvl III armor is capable of stopping rifle rounds and requires a steel or ceramic plate like previously suggested. Lvl IIIA is the high end threat level for concealable soft body armor. Every company that makes soft armor makes this threat level so it won't be hard to find some. The newer fibers make them extremely light and flexible (and a little more expensive).
You can get a Lvl IIIA Point Blank for a large male from Botach Tactical for about $380.
http://www.botachtactical.com/poinblancona.html
I've been wearing a PACA Lvl II for the past few years and will switch to this one as soon as I have the money. I got a buddy that wears one and he swears by them for comfort. Keep in mind that he works in Texas, climate similar although more humid than Oklahoma.
Whatever you get, wear the damn thing every time you wear your uniform. I'm having a hard time convincing the guys I work with (North Dakota, I migrated from Texas) that they can't choose when they get shot so they shouldn't try to pick and choose when to wear armor.
Check six and get home.