Most of the books about Theta are no longer beign printed, BUT you can sometimes find copies on them on eBay, Amazon, Barnes & Noble.com etc.
Here is a listing of those books:
Sixty Years in Kappa Alpha Theta by Estelle Riddle Dodge
We Who Wear Kites Vol. 1 1870-1956 by Carol Green Wilson
We Who Wear Kites Vol. 2 1956-1976
Kite Flight (if you ever find a copy/copies of this one let me know. I want a copy and a District officer I know wants one as well).
Currently you can purchase: Bound By Mighty Vow: Sisterhood and Women's Fraternities, 1870-1920 by Diana B.Turk from any online bookstore. I own this book and I loved reading it. Kappa Alpha Theta archives served as one of the primary sources for this book as well so you may find some Theta history here as well as general overall "fair and balanced" history of women's fraternities in general.
I believe (and someone correct me if I'm wrong) Kappa chapter has a book written about just Kappa chapter but I dont know the name or author off hand.
Other sources of historical information you may find are in the passworded section of the Kappa Alpha Theta website. If you dont know your member number you can email HQ and they will send it to you so you can gain access.
Also dont be afraid to ask our Fraternity historian/archives chair with specific questions as well.
Hope this helps.