You can get fitted at Presby Plano on the 3rd floor of the main hospital building in their boutique called A Mother's Gift -- it's a baby gift shop but also a nursing lactation consultation place with a full line of nursing bras... you can get fitted for the right size bra there. I will tell you though most of the bras are pricey (about $30), but honestly those are the only ones that have held up nicely and I will be able to use again for my next child. For info about A Mother's Gift, call ###-###-####.
The other cheap nursing bras I bought at Target or Kohl's had to be trashed. Once you know your size, I'd also shop at Motherhood Maternity at your local mall.
I also used a website called ... www.motherwear.com and they have many nice bras too. And nursing blouses that are camoflauged very well! Here's the link to their maternity bras ... http://www.motherwear.com/cat.cfm/cid/52
Too bad Victoria's Secret hasn't jumped on the maternity/nursing bra bandwagon! I'd be buying those bras! Let me know if you need more info....