My DH got some really nice "Charlie Harper" type shirts from Daddyos.com. They are really nice shirts and my DH is a big guy and they came in his size. I couldn't remember the name of the website so I had to google it and this website also came up, charlieharpershirts.com.
Pretty sure they are exclusively Nat Nast. My dad has a couple that he ordered from their website. Anyway, he always commented about Charlie wearing them on the show.