I've been struggling to compile _that_ libtiff for the last 24h with no success. Instead of posting my problems, I wanted to make sure first that there's no libtiff already patched for the PSP available. So with your answer, I feel I have green light to post my autoconf/libtool problems in compiling the oficial sources of libtiff.
Many libs haven't been compiled on the PSP since there was no demand for them. If you find anything, it's usually just a HowTo on compiling it yourself, like you're doing in the other thread. I did something similar with giflib, which also isn't in the repo.