pants are hard. JC penny is cheap and work OK for me. delias is more expensive but they have 00s and really short ones. Macy's sometimes has sales on their jeans and you would find 0 there. I can only fit their skinny jeans.
Shirts are easiest for me (forever 21, ross, Khols)
Bras - Victoria Secret, target is good too. (if you get VS credit card it is can be pretty cheap and you get free stuff often!)
shoes...i have to wear size 5 and I get boots or sandles. I sometimes look in the kids section if they are cute and mature. I would say Target for shoes.
I found some cute boots today at Charming Charlies size 5 tho.
Hope it helps.
It IS a pain to find things our size but it is possible! good lucks :)
Not sure about American stores, but a UK store that I've come across had a section just for petites, it's called Miss Selfridge. Maybe you should google this? I'm sure you'll find some national stores :)