I found a similar problem but with AMD64. It seems to me that alot of the mirrors are missing packages or parts of packages. For example I had to look far and wide for a mirror that even had RARCRACK. pkg_add died in the middle so I wound up downloading the ports tree and building it from source instead.
This may be related to your problem or not.....
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BSDForums.org refugee #27 
Multibooting with LILO 
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