http://funadvice.com/r/14tvgrhs0vm "8,969 retail units under 55 different banners in 15 countries"...
trouble is, you'd have to dig through their documentation (from there) to figure it out. Eg, are you counting only walmart branded stores OR any that they own & operate? B/c those are two different numbers.
At the end of fiscal year 2010 Walmart has over 4,300 stores and clubs in the U.S.
That was found via their investor information website under the "FAQ".