Jim & Rocky,
   Not all Walmarts carry components and parts.  There are 3 super centers in my area, and none of them carry any Brinkmann parts.  They have the smokers, fryers, etc, but no component or replacement parts.
   Perhaps you fellas live in a large metro area where the store's inventory is larger.  I had to order mine from Brinkman, and pay the price, but I felt it was worth it.  I also bought a couple other goodies while I was at it.  Seems like they had free shipping, and a gift in the box.  If you go the the Brinkmann web site, and select a smoker, then look in accessories, you can find it, and it will tell you what product it is used in.  It's kind of a difficult site to find a particular item on, but it's all there somewhere!
For your info:
 
Brinkmann web site 
select products, then "Outdoor cooking", then Smoke-N-Grill Stainless Steel, scroll down and select "Porcelain Coated Charcoal Pan".  That's the one.  This is actually the water pan for the Gourmet cooker/ charcoal pan for others.
   Brinkmann's site is kinda surprising.  First time I went there, I recognized all sorts of products I have either seen or used, but didn't associate the Brinkmann name.  Hope this helps.