Build a bear has really cute clothes! But if your baby is as tiny as mine, I have yet to find anything there that will fit. There is like 2 shirts I was able to alter to fit. but the others were way too big for him. Gus is 2.9 lbs. Good luck with your search. Here are 2 sites that I found.
http://www.thepetcompany.com/petco/express/baseball.htm <~~here is where I get Gus's jerseys
http://store.yahoo.com/petendipity/ad2302.html