I have two books for this, recommended to me by my teacher:
A tuneful introduction to 3rd position by Neil Mackay
and
Position changing on the violin by Neil Mackay
I've used these books on my own rather than with my teacher and i find them to be quite useful for learning to read in 3rd position. Another idea might be to get the ETA Cohen book 3, which i used to use in my lessons. It goes through a range of techniques but also has some exercises for 3rd position