These are all also free @ B&N, Sony (not available to Canadians), and Kobo (probably Borders, by extension).
For your 1-click convenience:
Part I
B&N,
Sony,
Kobo.
Part II
B&N,
Sony,
Kobo.
Part III
B&N,
Sony,
Kobo.
I'm not going to bother linking to Borders. They'll probably give you an error message when you try to add it directly from their listings and make you go through their desktop app instead.