I have done mega research on this topic.
Cosco carries my favorite brand of childrens clothes sometimes. It is agabang (don't try going to their web page, it is in a foreign language! LOL)
Also Chocolate Soup carries them! They are great romper type sleepwear for summer.
The Gap carries a Short John we love.
Gymboree has awesome baby jammies that zip up the front with no feet, also romper style (we don't do baby clothes with feet)
Right now they have the cutest aligator print one, and a shark one! TOO CUTE
JCPennys carries a brand,ummmm can't recall right now, that is great all the way up to 2T
Sears has some great deals on romper style cotton jammies
Hope this helps a little, I hate 2 piece sleepwear for babies, I can't stand the elastic marks on their tummies! Plus it tends to bring the cloth diaper down, and sometimes rolls down into their diaper and makes a PJ wick!