The original thread for this server is here:
http://openwrt.ksilebo.net/forum/viewtopic.php?t=150
and I got the thttpd-php_2.21b-1_wrt_mipsel.ipk package from this directory:
http://davidoffdotnet.net/openwrt/ipkg
which unfortunately is not available at the moment for a couple of reasons:
http://davidoffdotnet.net/openwrt/ipkg/MISSING_PKGS
which I believe I may have inadvertently had a some hand in:
http://openwrt.ksilebo.net/forum/viewtopic.php?t=195
Having said that, I just checked the licenses for both thttpd and for PHP and I *believe* that binary distribution is allowed, even though I would prefer not to pass along the binary without the source, if only to be able to easily check the integrity of the binary. Of course I would also like to be sure about the license. I'll check with Sam and see what he thinks. If nothing else it looks like he should have the files back up soon, otherwise I'll post them in my ipkg directory for you. I'll let you know as soon as I know.