Black is definately a hard colour to get for kids. Maybe ask Cai where she has bought some of Paris' clothes, she has some gorgeous black outfits
I do know of a fantastic online store that has black long sleeve t-shirts But they have pictures / writing on them. Maybe the owners shoudl look into doing some plain tops too!!

Dying things black isn't as easy as you would think, it's very hard to get it even and it looks a terrible if it's all splotchy.


ETA: I just PMed you some links