I couldn't find it directly at the site (the link just shows the index of the 16 original ebooks), but a bit of googling turned it up. They do have it in all four formats, but I remember there being some problem with the PRCs (maybe they didn't work because they expected a nonexistent PID?)
Links for freebies past the original 16:
The Last Cowboy (
EPub,
PDF,
PRC,
PDB)
A Family of Her Own
(
EPub,
PDF,
PRC,
PDB)
The Horseman's Son:
(
EPub,
PDF,
PRC,
PDB)