I must be about the same size as you, I swim in most XLs and standard larges aren't long enough.
As Newracer said, "tall" or "long" is the key.
I really like the Gap classic polos in LT. It can sometimes be hard to find the color you want in stock, but they are worth looking for. I buy them online.
Old Navy has tall sizes too, but their fabrics are generally really thin which is bad for concealment.
I'm still looking for tall Tshirts that are thick enough.
Let me know if you find any other good brands of polos or Tshirts.
If you willing to spend the money, Under Armour polos are the best ive had. They are pretty long, and comfy. But unless you find a good deal they are about $80.
My EDC: Handcuffs, Bandana, and Ball Gag.
If I'm ever at a party and the cops come to arrest people. Ill blindfold myself, throw the ball gag in, handcuff my hands, and hide in a closet. Police never arrest hostages!